Optical information recording medium, producing method thereof and method of recording/erasing/reproducing information

ABSTRACT

The present invention provides an optical information medium having excellent weather resistance and repeating characteristics. The optical information medium has a barrier layer between a protective layer and a recording layer. The barrier layer includes GeN or GeON, and at least one element selected from the group consisting of Al, B, Ba, Bi, C, Ca, Ce, Cr, Dy, Eu, Ga, H, In, K, La, Mn, N, Nb, Ni, Pb, Pd, S, Si, Sb, Sn, Ta, Te, Ti, V, W, Yb, Zn and Zr.

This application is a divisional of application Ser. No. 09/390,228,filed Sep. 3, 1999, now U.S. Pat. No. 6,821,707 which is acontinuation-in-part of application Ser. No. 08/815,301, filed Mar. 11,1997 now abandoned and Ser. No. 09/050,762, filed Mar. 30, 1998, nowabandoned which application(s) are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recording mediumprovided with an optically detectable information recording layer, theproducing method thereof and a method of recording/erasing/reproducinginformation.

2. Description of the Prior Art

A recording material thin film layer comprising a metal thin film and anorganic thin film is formed on a disc-shaped or a card-shaped substrate.A high energy beam focused on a micro light spot having a submicronorder diameter is irradiated onto the recording material layer, therebya local variation is generated on recording material layer. Thereby,such a technique that an information signal is stored is already wellknown. More specifically, when an optical magnetic material thin filmand a phase change material thin film are used for a recording layer, itis easy to rewrite the signal. Accordingly, this technique has beenactively studied and developed. For example, in case of the opticalmagnetic recording medium, a difference of a rotating angle on apolarized surface of a reflected light generated due to the differenceof a magnetization state is used as the record. Furthermore, in case ofthe phase change recording medium, an amount of a reflected lightrelative to a light having a specific wavelength in a crystalline stateis different from that in an amorphous state, thereby the difference isused as the record. A laser output is modulated between a record levelhaving a relatively higher power and an erasure level having arelatively lower power, and the modulated output is only irradiated on arecording medium. Thereby similarly to a magnetic disk, there is such acharacteristic that the record erasure and the record of a new signalcan be simultaneously performed (it is possible to overwrite therecord). The information signal can be rewritten for a short time.

Usually, the optical magnetic recording medium and the phase changerecording medium comprise, for example, a multi-layer film shown inFIG. 1. That is, on a substrate 1 comprising a resin plate of apolycarbonate and PMMA (polymethyl-methacrylate), a glass plate, or thelike, usually, a recording layer 3 having an optical absorptioncomprising the phase change material and the optical magnetic materialinserted between protective layers 2 and 4 comprising a dielectricmaterial is formed. Furthermore, a metallic reflecting layer 5comprising an alloy of Au and Al for increasing an optical absorptionefficiency on the recording layer 3 and for acting as a thermaldiffusion layer is formed on the protective layer 4. These layers aresequentially laminated by a sputtering method, a vacuum depositionmethod, or the like. Furthermore, an overcoat layer 6 is formed on anuppermost layer in such a manner that a scratch and dusts are notattached to these layers. Usually, a laser beam is incident from a sideof the substrate 1. In many cases, a front surface of the substrate 1 isprovided with a concave-convex groove track or a concave-convex pitsequence as guide means for guiding the laser beam to a predeterminedposition on the disk.

A function of each layer and a concrete example of materials formingeach layer are as follows.

In case of the recording layer 3, when the phase change material isused, chalcogenite thin film whose base comprises Te and Se, forexample, a Ge—Sb—Te alloy thin film, a Ge—Sb—Te—Se alloy thin film, anIn—Sb—Te alloy thin film, an Ag—In—Sb—Te alloy thin film, an In—Se alloythin film, and the like are reported. In the medium using such phasechange materials, the laser beam is irradiated, thereby the signal isrecorded and reproduced. As already described, while the power of thelaser beam is being modulated at a strong level and a weak level, thelaser beam is irradiated onto a revolving recording medium. A portionirradiated with the strong power is locally melt in an instant,thenceforth, the portion is quenched. Thereby the portion is amorphized,and the signal is recorded. Furthermore, at the portion irradiated witha relatively weak power, the amorphous-state portion is annealed,thereby the portion is crystallized, and the recorded signal is erased.In order to reproduce the signal, the power of the laser beam is reducedenough in such a manner that the recording film is not changed, and thelaser beam is irradiated. At this time, a strength of the reflectedlight is detected, and whether the portion irradiated with the laserbeam is in the crystalline state or the amorphous state is judged,thereby the signal is reproduced.

The functions of the protective layers 2 and 4 comprising a dielectricmaterial are, for example, as follows:

-   -   1) the recording layer is protected from an external mechanical        damage;    -   2) a thermal damage such as a roughness on the surface of the        substrate, a break of the recording layer and an evaporation,        etc. occurred due to repeatedly rewriting the signal are        reduced, thereby a repetition of rewriting the signal can be        increased;    -   3) an interference effect of a multipath reflection is used so        that an optical change can be enhanced;    -   4) an influence from an outside air is intercepted so that a        chemical change can be prevented.

As the material comprising the protective layer for satisfying the aboveobjects, heretofore, an oxide such as SiO₂, Al₂O₃ or the like, a nitridesuch as Si₃N₄, AlN or the like, an acid nitride such as Si—O—N or thelike (for example, disclosed in Japanese Patent Application Laid-openNo. 3-104038), a sulfide such as ZnS or the like, a carbide such as SiCor the like, or a mixed material such as ZnS—SiO₂ or the like (disclosedin Japanese Patent Application Laid-open No. 63-103453) is proposed, andone part of them is practically used.

Two layers are provided to the protective layer, thereby thecharacteristic thereof can be enhanced. The example of the phase changerecording medium is disclosed in Japanese Patent Application Laid-openNo. 5-217211. That is, the dielectric layer comprising the nitride (SiN,AlN) and the carbide (SiC) is used at the side contacted to the opticalrecording layer as the protective layer of the optical recording layerincluding Ag, and ZnS or a compound including ZnS is used as the outerlayer of the dielectric layer. The above SiN, SiC, AlN layer is used,thereby a combination of Ag included in the recording layer and S in theprotective layer is prevented. As disclosed in Japanese PatentApplication Laid-open No. 5-217211, a film thickness of the SiN, AlN,SiC layer is ranging from 5 nm to 50 nm. Furthermore, as disclosed inJapanese Patent Application Laid-open No. 6-195747, the protective layerhas two layers inserted between the recording layer and the substrate,where one layer contacted to the recording layer comprises Si₃N₄ layerand the other layer contacted to the substrate comprises ZnS—SiO₂ layer,thereby two dielectric layers are formed. The Si₃N₄ layer facilitates acrystallization of the phase change material layer.

The example of the optical magnetic recording medium is disclosed inJapanese Patent Application Laid-open No. 4-219650. Here, the dielectriclayer contacted to the substrate has two layers, and one layer contactedto the substrate is a silicon oxide film, thereby an addhesiveness ofthe substrate and the dielectric layer is enhanced. Furthermore, theother layer contacted to the recording layer comprises the compound ofthe carbide and the nitride, thereby it is possible to prevent acorrosion of the magnetic recording layer occurred due to that oxygenfrom the silicon oxide layer and water passing through the substrate arepenetrated into the recording layer. As disclosed in Japanese PatentApplication Laid-open No. 4-219650, preferably, the nitride comprisesSn—N, In—N, Zr—N, Cr—N, Al—N, Si—N, Ta—N, V—N, Nb—N, Mo—N and W—N, andthe film thickness thereof is ranging from 10 nm to 20 nm. Furthermore,as disclosed in Japanese Patent Application Laid-open No. 4-321948, inthe same view of Japanese Patent Application Laid-open No. 4-219650, thedielectric layer contacted to the substrate has two layers. Here, onelayer near the substrate comprises at least one kind of oxides selectedfrom a group of Si, Zr, Y, Mg, Ti, Ta, Ca and Al, thereby theadhesiveness of the dielectric layer and the substrate is enhanced.Furthermore, the other layer contacted to the optical magnetic recordingfilm comprises the nitride layer comprising at least one kind ofnitrides selected from the group of Si, Zr, Y, Mg, Ti, Ta, Ca and Al,thereby it is suppressed that oxygen and water from the oxide layer arepenetrated and diffused into the recording film layer. As disclosed inJapanese Patent Application Laid-open No. 4-321948, the film thicknessof the nitride layer is ranging from 50 nm to 200 nm.

It is known that the protective layer is formed of a complex materialcomprising different substances so as to provide the film with goodquality. For example, Japanese Laid-Open Patent Publication (Tokkai-Sho)No. 63-50931 discloses an example including a protective layer with goodquality such as excellent adhesiveness with a substrate by adding atleast either one of aluminum oxide and silicon oxide to a complexdielectric of aluminum nitride and silicon nitride and by defining therefractive index.

Japanese Laid-Open Patent Publication (Tokkai-Hei) No.2-105351 disclosesan example including a protective layer having excellent adhesivenesswith a substrate and excellent ductility formed of a complex dielectriccomprising a nitride of silicon and indium.

Furthermore, Japanese Laid-Open Patent Publication (Tokkai-Hei) Nos.2-265051, 2-265052 disclose examples including a protective layer formedof Si, N and an element having a smaller specific electric resistancethan Si, so that the protective layer is hardly cracked and protects therecording layer sufficiently.

In general, the reflecting layer 5 comprises a metal such as Au, Al, Cr,Ni, Ag or the like and the alloy based upon these metals, and thereflecting layer 5 is disposed in such a manner that a radiation effectand an effective optical absorption of the recording thin film can beobtained.

As described above, in general, a sputtering method, a vacuum depositionmethod or the like is used as the method of preparing the recordingmedium. Furthermore, a reactive sputtering method is used so that thenitride can be contained in the thin film.

For example, as the method of producing an ablation type write oncemedium, such a method that N is contained in the Te-containing recordinglayer by the reactive sputtering is disclosed in Japanese PatentApplication Laid-open No. 63-151486. As disclosed in Japanese PatentApplication Laid-open No. 63-151486, a mixed gas of Ar and nitride isdischarged relative to a telluric selenium alloy target. After therecording film containing tellurium, selenium and nitride on thesubstrate is formed by the reactive sputtering method, a nitrogen gas isintroduced, and a nitrogen plasma is generated, thereby a surface layerhaving a high nitrogen density than an inside of the recording layer isformed. The surface of the recording film is nitrided, thereby aweather-proofness and a sensitivity are enhanced, and further a powertolerance is increased. The nitrogen density of the nitride layer isranging from 2% to 10%, preferably, it is ranging from 2% to 20%.Preferably, the thickness of the surface layer is ranging about from 1nm to 10 nm.

Furthermore, the example of the ablation type recording material is alsodisclosed in Japanese Patent Application Laid-open No.63-63153. Thetarget comprising a material containing Te and Se is sputtered in anitriding-oxide gas, a nitric dioxide gas or a gas containing a nitricdioxide, thereby the layer containing Te, Se and N is formed in therecording layer.

Furthermore, as disclosed in Japanese Patent Application Laid-open No.4-78032, the surface of a metallic target is sputtered by Ar gas, and onthe surface of the metallic element substrate is reacted with oxygen gasor nitrogen gas, thereby a metallic oxide film or a metallic nitridefilm is formed.

Furthermore, although omitted in the drawings, in order that anoxidization of the optical information recording medium or an attachmentof dusts, etc. is prevented, such a structure that the overcoat layer isplaced on the metallic reflecting layer 5, such a structure that anultraviolet curing resin is used as an adhesive so that a dummysubstrate is laminated, or the like is proposed.

However, it is known that the phase change optical recording medium hasthe following problems. That is, when the thin film comprising amaterial whose base is Te, Se, etc. containing Ge, Sb, In, etc. is usedas the recording layer, and further the thin film comprising an oxidesystem material including such as SiO₂ representatively, the thin filmcomprising a sulfide system material including such as ZnSrepresentatively, or the thin film comprising a mixture system materialincluding ZnS—SiO₂ between the above two thin films is used as theprotective layer, a laser irradiation is carried out. Thereby, therecord and erasure of the information signal, and the like are repeated,thereby optical characteristics of the recording layer and theprotective layer (such as a reflectivity, an absorptivity and the like)are changed. Accordingly, such a phenomenon that a recordingcharacteristic or an erasure characteristic is changed. That is, thesignal is repeatedly rewritten, thereby the reflectance of the medium isreduced, an amplitude of the signal is gradually reduced, or a jittervalue at a marked position of a recording mark becomes larger, therebyan error rate of the recording signal becomes higher. Therefore, whenthe signal is reproduced, a readout error is occurred. Accordingly,there is such a problem that a possible times of rewriting is limited.

Principal causes of this change are as follows. That is, one cause isthat an S component and an O component are diffuse and penetrate fromthe protective layer to the recording layer, on the contrary, thecomponent such as Te, Se, etc. having a relatively high vapor pressureamong the components of which the recording layer consists of diffusefrom the recording layer to the protective layer. Furthermore, anothercause is that one part of the protective layer material is chemicallyreacted with the recording layer. It is considered that the change isoccurred due to either of the above causes, or a combination of theabove causes.

In fact, according to an experiment by inventors, etc., in the opticaldisk applying a Ge—Sb—Te recording film and a ZnS—SiO₂ protective layer,the S component is discharged from the protective layer due to the laserirradiation. Consequently, it is observed that an S atom is penetratedfrom the protective layer to the recording layer. Furthermore, it isalso observed that the other Zn atom, Si atom and O atom are alsodiffused to the recording layer. In this case, although it is assumedthat other elements are easy to move by a separation of the S atom, themechanism thereof is not clear.

The phenomenon and the mechanism have not been clearly reported. In casethat the nitride thin film including Si₃N₄ and AlN is used as theprotective layer, the S component is not discharged, differently fromthe above example. On the other hand, an adherence to the recordinglayer of such a nitride is lower than that of ZnS—SiO₂ film. Forexample, under an environment having a high temperature and a highhumidity, there is another problem that a peeling is occurred. That is,when oxide such as SiO₂, Ta₂O₅, Al₂O₃ and the like and nitride such asSl₃N₁ AlN and the like are used as a dielectric material, since such adielectric, material is less adhesive to a phase change type recordingmaterial, for example, under the high-temperature and high-humidityenvironment, the peeling and crack are occurred. Thereby, there isfurther problem that oxide such as SiO₂, Ta₂O₅, Al₂O₃ and the like andnitride such as Si₃N₄, AlN and the like cannot be applied to adielectric layer material.

A deterioration mechanism is summarized. In the first place, the morethe times of repeating is increased, the more the above atom diffusionand chemical reaction are proceeded. Consequently, a composition in therecording layer is largely varied, thereby variations of thereflectance, the absorption and the like, and the variation of therecording characteristic (an amorphization sensitivity) and the erasurecharacteristic (a crystallization sensitivity and a crystallizationrate) are actualized. It is supposed that in the protective layer,accompanied by the change of the optical characteristic, the compositionchanged, thereby such a change that a mechanical strength is reducedoccurs. It can be considered a ZnS—SiO₂ film widely applied as anexcellent protective layer has a high adhesiveness between theprotective layer and the recording layer and this results from theatomic diffusion. Furthermore, it is also considered that such aprotective layer substantially contains a limit of the repeating times.

Relating to a material containing Ag and S, that is, the elements whichare easy to chemically react, the method of suppressing the reaction isdisclosed in Japanese Patent Application Laid-open No. 5-217211.However, the following view is not disclosed in the above prior art.That is, relative to the phase change recording medium such as Ge—Sb—Tesystem, In—Sb—Te system and the like being developed for an applicationas the most possible material system, in order to enhance the cycleperformance thereof, the layer comprising the material such as nitride,nitriding-oxide, etc. is formed between a dielectric protective layerand a phase change recording layer. The formed layer acts as a barrierlayer for preventing an interdiffusion and the chemical reaction betweenthe recording layer and the protective layer. Furthermore, morespecifically, Ge—N or Ge—N—O is superior as the dielectric protectivelayer material which does not substantially have the above problem. Thismaterial has also an excellent performance as the barrier layer. This isnot also disclosed in the prior art.

SUMMARY OF THE INVENTION

That is, a layer structure for realizing an excellent repeatingcharacteristic and an excellent weather-proofness is not yet achieved.In order to solve the above problems, it is an object of the presentinvention to provide a medium structure for realizing a phase changeoptical recording medium having the excellent repeating characteristicand weather-proofness, the producing method thereof, and a method ofrecording and reproducing an information signal by using the recordingmedium.

In order to solve above problems, according to one aspect of the presentinvention, there is provided an optical information recording mediumcomprising a recording layer generating a reversible phase change whichcan be optically detected according to an irradiation of an energy beam,and a material layer which is named a barrier layer formed in contactwith at least one surface of the recording layer, wherein an atomicdiffusion and a chemical reaction occurred between the protective layerand the recording layer are suppressed by the barrier layer.

A material constituting the barrier layer (a barrier material) itselfcan be applied to a protective layer material as it is. In this case, itis expressed as “the protective layer using the barrier material”.

According to another aspect of the present invention, preferably, thereis provided an optical information recording medium, wherein a barriermaterial layer is disposed at both sides of a recording layer.

According to a structure in which the barrier material is applied to asubstrate side of the recording layer, an effect for suppressing theatomic diffusion and the chemical reaction between the recording layerand the protective layer is higher, thereby a cycle performance isenhanced. According to the structure in which the barrier material isapplied to the side opposite to the substrate of the recording layer,the effect for enhancing a stability of rewrite performance is higher,thereby a reliability is enhanced. Not only the structure in which thebarrier material is applied to both sides of the recording layercombines both characteristics, but also both performances are furtherenhanced.

According to further aspect of the present invention, preferably, thereis provided an optical information recording medium, wherein when thebarrier material is represented by M_(a)X_(b) (where, M denotes anaggregate of non-gas elements M₁, M₂, . . , and X denotes the aggregateof gas elements X₁, X₂, . . ), regarding a ratio of a gas componentb/(a+b), the ratio of the barrier material layer at the substrate sideis relatively higher than that of the barrier material layer at the sideopposite to the substrate.

According to further aspect of the present invention, preferably, thereis provided an optical information recording medium further comprising ametallic reflecting layer.

According to further aspect of the present invention, preferably, thereis provided an optical information recording medium, wherein theprotective layer using the barrier material” having a thin thickness of60 nm or less is applied between the metallic reflecting layer and therecording layer for a quenching. Thereby, since the number of layers canbe reduced, a preparing process can be simplified. Furthermore, since acooling effect is enhanced, thereby a thermal interference betweenrecording marks is reduced, an information signal can be denselyrecorded. That is, the structure is advantageous to a high densityrecording. More preferably, in this case, the barrier layer is alsoapplied to the substrate side of the recording layer. Thereby, it ispossible to obtain the medium which can realize a higher cycleperformance and a higher density recording.

According to further aspect of the present invention, preferably, thereis provided an optical information recording medium, wherein “thestructure (a rather slow cooling structure) necessary for a dielectriclayer having a thickness of 80 nm or more between the metallicreflecting layer and the recording layer, the barrier layer is appliedto at least one side of the recording layer. Thereby, usually, in therather slow cooling structure having a tendency of high heat-storingeffect and a large thermal damage, the cycle performance can be largelyenhanced.

According to further aspect of the present invention, there is providedan optical information recording medium, wherein the thickness of thebarrier layer is at least more than 1 nm to 2 nm. Thereby, the aboveeffect can be obtained. Preferably, the thickness is 5 nm or more.Thereby, even if a laser power used for recording is higher, the effectcan be obtained. Thereby, a further effect can be obtained. Furthermore,more preferably, the thickness is 20 nm or more. Thereby, a higherreproducibility can be obtained in preparing.

According to further aspect of the present invention, there is providedan optical information recording medium, wherein the barrier materiallayer containing Ge—N or Ge—N—O is used as the barrier material.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein when Ge—Nor Ge—N—O material layer is applied at both sides of the recording layeras the barrier layer or the protective layer, regarding a density of agas element in Ge—N or Ge—N—O layer, that is, (N+O)/(Ge+N+O), thedensity in Ge—N or Ge—N—O layer at the substrate side of the recordinglayer is relatively larger than that in Ge—N or Ge—N—O layer at the sideopposite to the substrate of the recording layer.

According to further aspect of the resent invention, preferably there isprovided an optical information recording medium, wherein Ge—Ncomposition region having a Ge density ranging from 35% to 90% isselected. More preferably, the range from 35% to 65% is selected.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein in casethat the a Ge—N layer is applied to the substrate side of the recordinglayer (at the side which a laser beam is incident on), the Ge densityranging from 35% to 60% is selected. In case that the Ge—N layer isapplied to the side opposite to the substrate of the recording layer,the Ge density ranging from 42.9% to 90% (preferably, 42.9% to 65%) isselected.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein in atriangular diagram in FIG. 5 showing three-element composition ofGe—N—O, Ge—N—O composition region is within a range surrounded by fourcomposition points, B1(Ge_(90.0)N_(10.0)),B4(Ge_(83.4)N_(3.30)O_(13.3)), G4(Ge_(31.1)N_(13.8)O_(55.1)),G1(Ge_(0.35) N_(0.65)). In this region, there are such effects that thecycle performance is enhanced and an erasure performance is enhanced.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein in casethat the Ge—N—O layer is applied to the substrate side of the recordinglayer (at the side which the laser beam is incident on), the regionsurrounded by four composition points D1(Ge_(60.0) N_(40.0)), D4(Ge_(48.8) N_(10.2) O_(41.0)), G1 (Ge_(35.0) N_(0.63)).G4(Ge_(31.1)N_(13.8)O_(55.1)) is appropriate. In case that the Ge—N—Olayer is applied to the side opposite to the substrate of the recordinglayer, the region surrounded by four composition points B1 (Ge_(65.0)N_(35.0)), B4 (Ge_(54.3) N_(9.1) O_(36.6)), F1 (Ge_(42.9) N_(57.1)), F4(Ge_(35.5) N_(12.9)O_(51.6)) is appropriate. In this case, preferably,the region surrounded by four composition points C1 (Ge_(65.0)N_(350.0)), C4 (Ge_(53.9) N_(9.2) O_(36.9)), F1 (Ge_(42.9) N_(57.1)), F4(Ge_(35.5) N_(12.9)O_(51.6)) is appropriate.

Similarly to the case of the Ge—N layer, when the Ge—N—O layer is formedat the side opposite to the substrate of the recording layer (at theside which the laser beam is not incident on), in a process of recordingand erasing, there is less possibility that a Ge atom is included in therecording layer. The layer can be also applied to the composition regionhaving a considerably high Ge density. On the contrary, when the Ge—N—Olayer is formed at the substrate side of the recording layer (at theside which the laser beam is incident on), there is more possibilitythat the Ge atom is included in the recording layer. It is notpreferable that the layer is applied to the composition region having aconsiderably high Ge density.

As described above, the Ge—N layer or the Ge—N—O layer is acted in sucha manner that the atomic interdiffusion and chemical reaction generatedbetween the recording layer and the protective layer usually comprisinga dielectric material are suppressed. There is such an advantage thatthe Ge—N layer or the Ge—N—O layer has a higher adhesiveness to therecording layer, compared to other nitride films such as Si₃N₄, AlN,etc. and a carbide film such as SiC, etc. The reason that the Ge—N layeror the Ge—N—O layer has a higher adhesiveness is as follows. Compared toother nitride films such as Si₃N₄, AlN, etc., the Ge—N layer or theGe—N—O layer enables to form the film with a relatively lower power at ahigh speed (for example, when a distance between a target and thesubstrate is 200 mm, if the target whose diameter is 100 mm is used, thefilm can be formed with 500 W at 40 nm to 50 nm/minute). Accordingly, itis assumed that since an internal stress in the film is lower, the Ge—Nlayer or the Ge—N—O layer has a higher adhesiveness. However, this isnot clear.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein a complexrefractive index value n+ik applies the Ge—N or Ge—N—O layer satisfyingthe range of 1.7≦n≦3.8 and 0≦k≦0.8. More preferably, when the barriermaterial layer is formed at the substrate side of the recording layer,the Ge—N or Ge—N—O layer satisfying the range of 1.7≦n≦2.8 and 0≦k≦0.3is applied. When the barrier material layer is formed at the sideopposite to the substrate, the Ge—N or Ge—N—O layer satisfying the rangeof 1.7≦n≦3.8 and 0≦k≦0.8 is applied. An optical constant is changedaccording to a ratio of O to N in the film, when O is less, the opticalconstant becomes larger. When O is more, the optical constant becomessmaller.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein a materialthin film whose main component is Ge—Sb—Te is used as the recordinglayer.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein thematerial thin film whose main component is ZnS—SiO₂ is used as adielectric protective layer material used together with the barrierlayer.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein a materiallayer containing a main component comprising a nitride or anitriding-oxide having at least one kind of element selected from theelements constituting the recording layer is used as the barriermaterial layer.

In general, although a nitride material is less adhesive to achalcogenite material, the barrier layer containing a nitride ornitriding-oxide of the element included in the recording layer is used,thereby the elements in the barrier layer is common to the componentelement in the recording layer. Accordingly, the adhesiveness can beenhanced. In this case, it is possible to suppress the interdiffusionand the chemical reaction between the recording layer and the protectivelayer whose main component is the dielectric material. Thereby, thephase change optical recording medium having the excellent repeatingperformance and excellent weather-proofness can be realized.

According to further aspect of the present invention, preferably thereis provided an optical information recording medium, wherein at leastone surface of the recording layer is nitrided or nitric-oxidized,thereby the barrier layer is formed.

In this case, since the recording layer and the nitride layer or thenitric-oxide layer have the films having a high continuity to eachother, there is less problem relating to the adhesiveness. Accordingly,the optical information recording medium having the excellent repeatingperformance and the excellent weather-proofness can be obtained.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium for solving the aboveproblems, comprising a vacuum deposition method, a DC sputtering method,a magnetron sputtering method, a laser sputtering method, an ion platingmethod, a CVD method and the like.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, wherein asputtering method is used, a single target comprising the main componentM of the barrier material, a nitride target comprising M, a nitric-oxidetarget, or an oxide target is used in order that the barrier materiallayer is formed, so that a reactive sputtering is carried out in a mixedgas of a rare gas and the gas containing a nitride component or themixed gas of the gas containing the rare gas and the nitride componentand the gas containing an oxide component, thereby the barrier materiallayer is formed.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinAr and Kr are used as the rare gas.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinN₂ is used as the gas containing the nitride component, and O₂ is usedas the gas containing the oxide component.

When the barrier material layer is formed at either sides of therecording layer, an N₂ density in case that the barrier material layeris formed at the side opposite to the substrate of the recording layeris highly set than that in case that the barrier material layer isformed at the substrate side of the recording layer. Thereby, thestructure having a further higher weather-proofness can be obtained.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinGe is used as the main component M of the barrier material, a Ge target,a Ge—N target, a Ge—N—O target or a Ge—O target is used so that thereactive sputtering is carried out, thereby the barrier material layeris formed. More preferably, a Ge₃N₄ composition is used as the Ge—Ntarget, a GeO composition is used as the Ge—O target, and Ge₃N₄—GeOmixed target is used as the Ge—O—N target. According to further aspectof the present invention, a method of preparing an optical informationrecording medium, more preferably, wherein Ge is used as the maincomponent M of the barrier material, when the reactive sputtering iscarried out, a total pressure of a sputter gas is more than 1 mTorr, andit is 50 mTorr or less. Within this range, a high sputter rate and astable discharge can be obtained.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinGe is used as the main component M of the barrier material, when thereactive sputtering is carried out, the sputter gas is the mixed gascontaining at least Ar and N₂, a partial pressure ratio of N₂ is rangingfrom 5% to 60%. Thereby, a better repeating performance and a betterweather-proofness can be obtained. In this case, when the barrier layeris used at the substrate side of the recording layer, the partialpressure ratio of N₂ is ranging from 12% to 60% (preferably, 50% orless). Furthermore, when the barrier layer is used at the side oppositeto the substrate, the partial pressure ratio of N₂ is ranging from 5% to60% (preferably, 40% or less, more preferably, 33% or less).

Regarding the repeating performance, when a nitride partial pressure inthe sputter gas is low, since much surplus Ge not combined to a nitrogenexists in the protective layer, the composition in the recording film ischanged, accompanied with rewriting the signal, thereby a bettercharacteristic cannot be obtained. Furthermore, when the nitrogenpartial pressure in the sputter gas gets too high, much surplus nitrogenexists in the film, thereby similarly to the above case, the betterrepeating characteristic cannot be obtained.

Regarding the weather-proofness (adhesiveness), when the nitrogenpartial pressure in the sputter gas is high and much surplus nitrogenexists in the film, after an acceleration test, a peeling is occurred.However, when the nitrogen partial pressure is low and the surplus Genot combined to the nitrogen exists, the peeling is not occurred. It isassumed that since Ge contributes to a combination with the recordingfilm, the peeling is not occurred.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinGe is used as the main component M of the barrier material, when thereactive sputtering is carried out, the sputter gas is the mixed gascontaining at least Ar and N₂ a sputter power density is more than 1.27W/cm², and a film forming rate is 18 nm/minute or more.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinGe is used as the main component M of the barrier material, when thereactive sputtering is carried out, the sputter gas is the mixed gascontaining at least Ar and N₂ the film is formed in such a manner thatthe complex refractive index value n+ik may satisfy the range 1.7≦n≦3.8,0≦k≦0.8. More specifically, when the barrier material layer is formed atthe substrate side of the recording layer, such a film forming conditionas to satisfy the range 1.7≦n≦2.8, 0≦k≦0.3 is selected. When the barriermaterial layer is formed at the side opposite to the substrate, such afilm forming condition as to satisfy the range 1.7≦n≦3.8, 0≦k≦0.8 isselected.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinat least one element among the materials constituting the recordinglayer is used as the main component of the barrier material layer, itssingle element target, its nitride target, its nitriding-oxide target orits oxide target is used, so that the reactive sputtering is carried outin the mixed gas of the rare gas and the gas containing the nitrogencomponent or the mixed gas of the rare gas and the gas containing thenitrogen component and the gas containing the oxygen component, therebythe film is formed.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinthe material itself constituting the recording layer is used as it is asthe main component of the barrier material layer, the target for formingthe recording layer, its nitride target, its nitriding-oxide target, orits oxide target is used, so that the reactive sputtering is carried outthe mixed gas of the rare gas and the gas containing the nitrogencomponent or in the mixed gas of the rare gas, the gas containing thenitrogen component and the gas containing the oxygen component, therebythe film is formed.

According to further aspect of the present invention, a method ofpreparing an optical information recording medium, preferably, whereinthe material itself constituting the recording layer is used as it is asthe main component of the barrier material layer, in at least either arecording layer formation start time or a recording layer formationcompletion time, either a process of forming the recording layer inwhich the density of the gas containing the nitride component in thesputter gas is enhanced, or a process of forming the recording layer inwhich the densities of the gas containing the nitride component and thegas containing the oxide component are enhanced is used, thereby therecording layer formation can be achieved.

According to the above processes, a supply of the gas constituting thenitride component and the oxide component may be stopped when arecording layer portion is formed in the recording layer formationprocess.

An optical information recording medium of one embodiment in the presentinvention includes a barrier layer, a first protective layer, and arecording layer generating a reversible phase-change which can beoptically detected according to an irradiation of an energy beam. Thebarrier layer is formed between the first protective layer and therecording layer and in contact with the first protective layer and therecording layer. The barrier layer includes either one selected from thegroup consisting of GeN and GeNO, and at least one element selected fromthe group consisting of Al, B, Ba, Bi, C, Ca, Ce, Cr, Dy, Eu, Ga, H, In,K, La, Mn, N, Nb, Ni, Pb, Pd, S, Si, Sb, Sn, Ta, Te, Ti, V, W, Yb, Znand Zr.

In an optical information recording medium of another embodiment in thepresent invention, the barrier layer is formed between the firstprotective layer and the recording layer and in contact with the firstprotective layer and the recording layer. The barrier layer is composedof a barrier material having a non-stoichiometric composition.

An optical information recording medium of one embodiment in the presentinvention includes a recording layer having reversibly changeableoptical characteristics and a Ge-containing layer comprising either oneselected from the group consisting of GeXN and GeXON as a maincomponent, where X is at least one element selected from the groupconsisting of elements belonging to Groups IIIa, IVa, Va, Via, VIIa,VIII, Ib and IIb and C. This makes it possible to provide a mediumhaving excellent weather resistance and excellent characteristics inrepetitive recording.

According to another aspect of the present invention, a method forproducing an optical information recording medium includes the steps of:forming a recording layer having reversibly changeable opticalcharacteristics, and forming a Ge-containing layer comprising either oneselected from the group consisting of GeXN and GeXON as a maincomponent, where X is an element as described above. The Ge-containinglayer is produced by reactive sputtering with a target including atleast Ge and X in a mixed gas comprising a rare gas and nitrogen. Thismakes it possible to produce efficiently an optical informationrecording medium having excellent weather resistance and excellentcharacteristics in repetitive recording.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a conventional structure of aphase change optical recording medium comprising four layers.

FIG. 2 is a cross-sectional view showing an structure example of anoptical information recording medium according to the present invention.

FIG. 3 is a cross-sectional view showing another structure example ofthe optical information recording medium according to the presentinvention.

FIG. 4 is a cross-sectional view showing another structure example ofthe optical information recording medium according to the presentinvention.

FIG. 5 is a composition diagram for explaining an appropriatecomposition range of a Ge—N layer or a Ge—N—O material layer applied tothe optical information recording medium according to the presentinvention.

FIG. 6 shows a structure example of an apparatus of preparing theoptical information recording medium according to the present invention.

FIG. 7 shows an example of a laser modulation waveform for recording andreproducing au information signal relative to the optical informationrecording medium according to the present invention.

FIG. 8 shows another example of a laser modulation waveform forrecording and reproducing an information signal relative to the opticalinformation recording medium according to the present invention.

FIG. 9 shows another structure of apparatus of preparing the opticalinformation recording medium by using the present invention.

FIG. 10 shows a difference of a repeating characteristic by using asputter gas pressure.

FIG. 11 shows the difference of the repeating characteristic by usingthe sputter gas pressure.

FIG. 12 shows a difference of an adhesiveness by using the sputter gaspressure.

FIG. 13 shows the difference of the adhesiveness by using the sputtergas pressure.

FIG. 14 shows a relationship between a nitrogen partial pressure in thesputter gas and an optical constant.

FIG. 15 shows the relationship between the nitrogen partial pressure inthe sputter gas and the optical constant.

FIG. 16 shows a relationship between a total sputter gas pressure andthe optical constant.

FIG. 17 is a cross-sectional view illustrating an exemplary structure ofa layer of an optical information recording medium of the presentinvention.

FIG. 18 is a ternary phase diagram of (GeX), O and N showing apreferable composition range of a diffusion preventing layer in theoptical information recording medium of the present invention.

FIG. 19 is a view illustrating an exemplary film-forming apparatus ofthe optical information recording medium of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of an optical information recording medium according tothe present invention is shown in FIG. 2. FIG. 2 shows the embodiment incase that a barrier layer is used at a substrate side of a recordinglayer.

According to the embodiment, a substrate 1 is a disc-shapedpolycarbonate resin substrate having a thickness of 0.6 mm and adiameter of 120 mm. Since a polycarbonate has such merits as a lowhumidity, a low cost and the like, the polycarbonate is superior as amaterial used for the substrate. Aside from the polycarbonate resin, aglass, an acrylic resin, a polyolefin resin, a vinyl chloride and thelike can be also used. Although a metal can be also used, the mediummust be designed in such a manner that a light is incident from the sidewhere a film is formed. Any way, a kind of the substrate is not limitedto the present invention.

A surface of the substrate is optically sufficiently flat. Furthermore,a spiral-shaped concave-convex groove track 7, for example, having adepth of 70 nm, a groove portion width of 0.74 μm and a land portionwidth of 0.74 μm is formed all over the surface where a multi-layer filmis formed. The concave-convex shape of the groove is operated as aguide, thereby a laser beam for recording and reproducing an informationsignal can be moved to an optional position. As a method of guiding thelaser beam, a continuous servo method using the spiral-shaped groove ora concentrically formed groove and a sample servo method tracing aperiodically arranged signal pit sequence are known. According to themethod of guiding the laser beam, although the groove is appropriatelyformed on the substrate 1, this does not also relate to a substance ofthe present invention.

According to the above embodiment, sequentially a protective layer 2comprising a ZnS—SiO₂ (SiO₂: 20 mol %) mixture layer, a barrier layer 8containing Ge—N or Ge—N—O, a recording layer 3 comprising a Ge₂Sb₂₃Te₅alloy thin film, a protective layer 4 comprising a ZnS—SiO₂ (SiO₂: 20mol %) mixture layer and a metallic reflecting layer 5 is formed on asurface where the concave-convex groove track 7 of the substrate 1 isformed by a sputter method. An ultraviolet curing resin is used as anadhesive layer 9, thereby the same resin plate as the substrate 1 islaminated as a defense plate 10. When the barrier layer 8 is Ge—N, in anorder from the protective layer 2 to the metallic reflecting layer 5,the thickness of each layer is sequentially 91 nm, 5 nm, 20 nm, 18 nmand 150 nm, respectively. When the barrier layer 8 is Ge—N—O, similarly,the thickness of each layer is sequentially 86 nm, 20 nm, 20 nm, 18 nmand 150 nm, respectively.

In general, the material forming the protective layers 2 and 4 is adielectric material, which is sometimes called a dielectric protectivelayer. Aside from ZnS—SiO₂, the materials which are conventionally usedfor the protective layer of the optical recording medium can be appliedto the protective layer as it is. For example, an oxide layer comprisinga single oxide or a compound oxide etc. such as Al, Mg, Si, Nb, Ta, Ti,Zr, Y, etc., a nitride layer comprising a nitride such as Al, B, Nb, Si,Ta, Ti, Zr, etc., a sulfide layer comprising a sulfide such as ZnS, PbS,etc., a serenide layer comprising ZnSe, etc., a carbide layer comprisingSiC, etc., a fluoride comprising CaF₂, LaF, etc., or a mixture of theabove materials such as a material layer comprising ZnSe—SiO₂, Si—N—O,etc. can be used.

The material forming the recording layer 3 is a phase change material tobe changed into a reversible state by receiving an irradiation of anenergy beam such as a laser beam, etc. More specifically, preferably,the material is reversibly changed between an amorphous state and acrystalline state by the irradiation of the laser light beam. Typically,a system containing Ge—Sb—Te, Ge—Te, In—Sb—Te, Sb—Te, Ge—Sb—Te—Pd,Ag—Sb—In—Te, Ge—Bi—Sb—Te, Ge—Bi—Te, Ge—Sn—Te, Ge—Sb—Te—Se, Ge—Bi—Te—Se,Ge—Te—Sn—Au, Ge—Sb—Te—Cr, In—Se, In—Se—Co and the like, or the systemresulted from adding a gas admixture such as oxygen, nitrogen, etc. tothese systems can be used.

When these thin films are formed, the thin films are in the amorphousstate. When the films absorbs an energy such as the laser beam, etc.,the films are crystallized. If the films are practically used as therecording medium, the recording film being in the amorphous state whenthe film is formed is previously crystallized by using such a method asa laser beam irradiation, a flush light irradiation, or the like. Thelaser beam is thinly focused, and the crystallized recording film isirradiated with the focused light beam. Accordingly, the irradiatedportion is amorphized, so that the optical constant is changed, therebythe record is carried out. By the above change, the changed portionwhere the above record is carried out is irradiated with such a weakenedlaser beam not as to further change the recording layer. A variation ofa reflecting light strength or the variation of a transmitted lightstrength is detected, thereby the information is reproduced. When theinformation is rewritten, the laser light beam is irradiated, and theamorphous portion is re-crystallized, thereby a recording mark iserased. After the erasure, a new recording mark is formed. As describedbelow, such an overwrite that an erasure operation and a recordingoperation are carried out during one rotation of the recording mediumcan be performed.

As described above, the material layer located between the protectivelayer 2 and the recording layer 3 as the barrier layer 8 is operated insuch a manner that an atomic diffusion and a chemical reaction betweenthe recording layer and the protective layer are prevented. Compared tothe recording layer, the material layer is needed to comprise thematerial having a higher melting point and a higher density.Furthermore, it is necessary that the material layer comprises thematerial which is hard to react with the material constituting therecording layer and the dielectric protective layer and to generate theatomic diffusion. Moreover, it is necessary that the material layercomprises the material which is not peeled from any layers and furtheris hard to generate a crack, etc. For example, the material providedwith the above characteristic among the nitride, the oxide, the carbide,the nitriding-oxide, an carbide of oxygen, a carbide of nitrogen and thelike is appropriate. Preferably, any material has slightly less oxygenand nitrogen than a stoichiometric compound composition. That is, forexample, when a stoichiometric nitrogen compound composition of theelement M and the nitriding-oxide are defined as M_(a)N_(b),M_(a)N_(b)—M_(c)O_(d) (where, a, b, c and d denote a natural number),the composition of the material layer used for the barrier layer isrequired to be expressed as M_(a)N_(b1) (b1≦b) andM_(a)N_(b1)—M_(c)O_(d1) (b1≦b) and d1≦d). More specifically, when thebarrier layer is applied at the side opposite to the substrate of therecording layer, preferably, M_(a)N_(b2) (b2≦b) andM_(a)N_(b2)—M_(c)O_(d2) (b2≦b and d2≦d).

Accordingly, even in case of such a composition as Si—N, Al—N, Si—O—N,or the like, the composition is expressed as Si₃Nm₁(m₁≦4, preferablym₁<4), AlNm₂ (m₂≦1, preferably m₂<1), Si₃Nm₃—SiOm₄ (m₃≦4 and m₄<2,preferably m₃<4 and m₄≦2, or m₃≦4 and m₄≦2), thereby there is increaseda possibility that the composition can be applied to the barrier layer.

Furthermore, when the barrier layer is formed at both the sides of therecording layer, an adhesiveness to the recording layer at the substrateside is different from that at the side opposite to the substrate. Thesubstrate side of the recording layer has a relatively highadhesiveness, and the opposite side has a low adhesiveness. From anexperimental result, when the barrier layer is formed at the substrateside of the recording layer, it is largely shifter from thestoichiometric composition. That is, when the barrier material isrepresented by M_(a)X_(b) (where, M denotes an aggregate of non-gaselements M₁, M₂, . . , and X denotes the aggregate of gas elements X₁,X₂, . . ), regarding a ratio of a gas component b/(a+b), the ratio ofthe barrier material layer at the substrate side is relatively higherthan that of the barrier material layer at the side opposite to thesubstrate. Accordingly, the medium having an excellent weather-proofnesscan be constructed.

Here, typically, the example using Ge—N or Ge—N—O is shown.

A Ge—N layer or a Ge—N—O layer includes at least Ge and N, or Ge, N andO. The Ge—N layer or the Ge—N—O layer may also include other elementssuch as Ge—Si—N—(O), Ge—Sb—N—(O), Ge—Cr—N—(O), Ge—Ti—N—(O), or the like.The other elements are, for example, Al, B, Ba, Bi, C, Ca, Ce, Cr, Dy,Eu, Ga, H, In, K, La, Mn, N, Nb, Ni, Pb, Pd, S, Si, Sb, Sn, Ta, Te, Ti,V, W, Yb, Zn, Zr, or the like.

Furthermore, as described below, the material forming the barrier layermay be replaced by the nitride and the nitriding-oxide of the materialcomposing recording layer. For example, when the main component of therecording layer consists of the elements among Ag, In, Sb and Te, abarrier layer can be Ag—N—(O), Sb—N—(O), In—N—(O), Te—N—(O) or a mixtureof them such as Ag—Sb—N—(O). When the main component of the recordinglayer is Te—Si—Ge, the barrier layer can be Si—N—(O), Ge—N—(O), Te—N—(O)or the mixture of them, for example, Ge—Si—N—(O). Cr and Al are added toGe—N and Ge—N—O, thereby the adhesiveness can be enhanced. Morespecifically, the addition of Cr enables to obtain a remarkable effect.At an additive density of about 5% or more, the adhesiveness can beenhanced. A preparing condition which can form the barrier layer havingan excellent adhesiveness is expanded. When the additive density exceeds50%, the cycle performance tends to be reduced.

The reflecting layer 5 comprises the material having a high reflectanceand a low corrosiveness. Instead of an Al—Cr alloy, a single Au, Al, Ag,Pd, Ni, Cr, Ta, Ti, Si, Co, etc. or the alloy whose base consists ofthem can be used. For example, Au—Cr, Au—Co, Al—Ta, Al—Ti, Ag—Cr, Ni—Cr,Au—Pd, and the like are preferable.

According to the above explanation, as a position where the barrierlayer is applied, such an example that the barrier layer is applied tothe interface between the dielectric protective layer at the substrateside and the recording layer is shown. Aside from the example of FIG. 2,there are different variations shown in FIGS. 3A to 3H and FIGS. 4A to4H as another example of FIG. 2. The shape of the groove, a contactlayer and the defense plate shown in FIG. 2 are omitted. Although thestructure of FIG. 3A is the same as that of FIG. 2, for simplify by acomparison among FIG. 3A and FIGS. 3B to 3H, FIG. 3A is again shown.

For example, when the barrier layer is used, even if not only thebarrier layer is used at the substrate side of the recording layer asshown in FIG. 3A, but also the barrier layer is used at the reflectinglayer side (shown in FIG. 3B) or at both sides (shown in FIG. 30, asimilar effect can be obtained. Furthermore, even if this layer isapplied all over a lower protective layer (shown in FIG. 3D), all overan upper protective layer (shown in FIG. 3E), or all over the lower audupper protective layers (shown in FIG. 3F) not as the barrier layer, butas the protective layer using the barrier material, the similar effectcan be obtained. For example, in FIG. 3F, the total dielectricprotective layers 2 and 4 at both sides of the recording layer 3 areformed by the material layer containing the barrier material, Ge—N orGe—N—O. In this case, this material layer has a numeral 8.

Furthermore, according to such a structure that the barrier layer(where, a Ge—N layer or a Ge—N—O layer) is used at the substrate side ofthe recording layer 3 and the total protective layer 4 comprises thebarrier material (where, the Ge—N layer or the Ge—N—O layer) at the sideof the reflecting layer 5 (shown in FIG. 3G), the similar effect can beobtained. According to such a structure that the total protective layer2 comprises the barrier material (where, the Ge—N layer or the Ge—N—Olayer) at the substrate side and the barrier layer (where, the Ge—Nlayer or the Ge—N—O layer) is applied at the reflecting layer side(shown in FIG. 3H), the similar effect can be obtained.

The upper protective layer is thinned, thereby the structure is designedin such a manner that the distance between the recording layer and themetallic reflecting layer is reduced. This structure is called aquenching structure. According to the quenching structure, if two ormore layers are formed at the upper side, since very thin layers must bedeposited, two or more layers are not preferable in view of an accuracyadministration of a film thickness, thereby it is difficult to prepare.In this case, the upper side comprises a single Ge—N layer or Ge—N—Olayer, thereby there is generated such a merit that it is easy toprepare.

FIG. 4 shows the structure when the reflecting layer is removed from thestructure in FIG. 3. FIGS. 4A to 4H correspond to FIGS. 3A to 3H,respectively. Furthermore, according to the structures shown in FIGS. 3and 4, in various views, such a structure that a semitransparentreflecting layer comprising Au and a semiconductor material (forexample, Si, Ge or the alloy whose base is Si, Ge) is added to thesubstrate side (the side which the light is incident on) of therecording layer can be used (not shown).

FIGS. 3 and 4 show such a structure that an uppermost layer is providedwith the overcoat layer 6. The overcoat layer 6 is disposed in orderonly to suppress an influence due to water, dusts and the like relativeto the protective layer and the recording layer of the opticalinformation recording medium. Accordingly, for example, such a structurethat a dummy substrate is laminated, such a structure that two platesare laminated with the over coat layer surface faced to an inner side,or the like is appropriately used according to a usual method.Furthermore, although the drawing is omitted, in order to laminateplates, a hot melt adhesive and an adhesive of the ultraviolet curingresin or the like are applied.

In order that the cycle performance can be enhanced, more effectively,the barrier layer 8, that is, the Ge—N layer or the Ge—N—O layer isformed at the substrate 1 side of the recording layer 3. Since the laserbeam is incident on the substrate side, a temperature at the substrateside tends to rise, thereby the composition change is easy to generate.Accordingly, it is assumed that the effect of the barrier layer becomesconsiderable.

Furthermore, in another view, when the barrier layer, that is, the Ge—Nlayer or the Ge—N—O layer is formed at the reflecting layer side of therecording layer, in addition to such a merit as to enhance the cycleperformance, such a merit as to enhance the erasure performance can beobtained. This relates to the following phenomenon. That is, when therecording layer is irradiated with the laser beam so that the film isamorphaized, in general, a solidification starts from the portion whosetemperature is lower. That is, it is assumed that the structure of therecording film composition and the interface at the side (usually, thereflecting layer side) where a cooling starts is a principal factor fordetermining the condition of a generated amorphous solid. That is, it isassumed that the barrier layer enables to suppress the atomic diffusionfrom the protective layer to the recording layer, the recording filmcomposition at the interface is also held in a cycle recording.

Accordingly, since the substrate 1 comprises the material such as themetal in which the light cannot be transmitted, when the light cannot beincident from the substrate side, note that this case is contrary to theabove description. That is, in this case, in order that the cycleperformance may be enhanced, effectively, the barrier layer, that is,the Ge—N layer or the Ge—N—O layer is formed at the side opposite to thesubstrate 1 of the recording layer 3. On the other hand, in order thatthe erasure performance may be enhanced, effectively, the barrier layer,that is, the Ge—N layer or the Ge—N—O layer is formed at the substrate 1side of the recording layer 3. Any way, if the Ge—N layer or the Ge—N—Olayer is formed at both sides of the recording layer, the above twomerits can be simultaneously achieved.

Table 1 shows a layer structure corresponding to FIGS. 3A to 3H andFIGS. 4Ato 4H. In the table, Sub denotes a substrate, DL denotes aprotective layer, BL denotes a barrier layer (GeNO), AL denotes arecording layer, RL denotes a reflecting layer, and OC denotes anovercoat layer. Furthermore, in the protective layer, the layer applyingthe barrier material, that is, the Ge—N layer or the Ge—N—O layer isrepresented by DL(GeNO), and the layer not applying the barrier materiallayer is represented by only DL.

TABLE 1 An example of layer structures of the recording medium FIG.layer structures 3A Sub DL BL(GeNO) AL DL RL OC 3B Sub DL AL BL(GeNO) DLRL OC 3C Sub DL BL(GeNO) AL BL(GeNO) DL RL OC 3D Sub DL(GeNO) AL DL RLOC 3E Sub DL AL DL(GeNO) RL OC 3F Sub DL(GeNO) AL DL(GeNO) RL OC 3G SubDL BL(GeNO) AL DL(GeNO) RL OC 3H Sub DL(GeNO) AL BL(GeNO) DL RL OC 4ASub DL BL(GeNO) AL DL OC 4B Sub DL AL BL(GeNO) DL OC 4C Sub DL BL(GeNO)AL BL(GeNO) DL OC 4D Sub DL(GeNO) AL DL OC 4E Sub DL AL DL(GeNO) OC 4FSub DL(GeNO) AL DL(GeNO) OC 4G Sub DL BL(GeNO) AL DL(GeNO) OC 4H SubDL(GeNO) AL BL(GeNO) DL OC

Next, as a typical barrier material, an appropriate composition range ofthe Ge—N layer or the Ge—N—O layer will be described below. FIG. 5 is atriangular diagram showing the composition range of the Ge—N layer orthe Ge—N—O applied to the present invention. In the appropriatecomposition of the Ge—N material which does not contain oxygen, the Gedensity has a lowest limit value of 35% to 40%. If the lowest limitvalue is reduced to less than 35% to 40%, the adhesiveness to therecording layer is reduced. According to an acceleration environmenttest, a peeling phenomenon are exhibited.

Furthermore, the Ge density has a supremum value of about 90%. If thesupremum value exceeds 90%, in a process of repeating recording anderasing, Ge is included in the recording film, thereby the cycleperformance tends to be reduced. The appropriate Ge density in case thatthe Ge—N layer is formed at the substrate side of the recording layer ismore or less different from that in case that the Ge—N layer is formedat side opposite to the substrate. The latter is little more highly setthan the former, thereby the adhesiveness is higher.

For example, the appropriate region of the Ge density of the former is35% to 60%, on one hand, the appropriate region of the latter is 40% to90% (preferably, 40% to 65%). When the former and the latter are formedunder the same condition, the appropriate Ge density is ranging from 40%to 60%. According to the present invention, since it is not necessarythat both of them are formed under the same condition, the appropriateGe density whose is within the range from 35% to 90% (preferably, from35% to 65%) is the effective composition region. Within the range from65% to 90%, the cycle performance tends to be relatively reduced.

Ge—N—O system containing oxygen is described below. An averagecomposition ratio of Ge to N to O in the Ge—N—O protective layer isshown in the triangular diagram showing the three-element compositionGe—N—O in FIG. 5. The average composition ratio can be explained byusing each composition point, that is, A1, B1 to B5, C1 to C5, D1 to D5,E1 to E5, F1 to F5, G1 to G5 and H1 to H3.

B2 (Ge_(89.7) N_(9.8) O_(0.5)), B3(Ge_(86.6) N_(6.7) O_(6.7)),B4(Ge_(83.4) N_(3.3) O_(13.3)), C2(Ge_(64.4) N_(33.8) O_(1.8)),C3(Ge_(58.8) N_(20.6)), C4(Ge_(53.9) N_(9.2) O_(36.9)), D2(Ge_(59.5)N_(38.0)), D3(Ge_(53.8) N_(23.1) O_(23.1)), D4(Ge_(48.8) N_(10.2)O_(41.0)), E2(Ge_(4.96) N_(47.9) O_(2.5)), E3(Ge_(45.4) N_(27.3)O_(27.3)), E4(Ge_(42.3) N_(11.5) O_(46.2)), F2(Ge_(42.4) N_(54.7)O_(2.9)), F3(Ge_(38.4) N_(30.8) O_(30.8)), F4(Ge_(35.5) N_(12.9)O_(51.6)), and G2(Ge_(34.8) N_(62.0) O_(3.2)), G3(Ge_(32.6) N_(33.7)O_(33.7)), G4(Ge_(31.1) N_(13.8) O_(55.1)) are defined as thecomposition points at which the following composition lines crosses oneanother. The composition lines are as follows:

-   -   a composition line B1–B5 connecting the composition point        B1(Ge_(90.0) N_(10.0)) to the composition point B5(Ge_(80.0)        N_(20.0)),    -   a composition line C1–C5 connecting the composition point        C1(Ge_(65.0) N_(35.0)) to the composition point C5(Ge_(50.0)        N_(50.0)),    -   a composition line D1–D5 connecting the composition point        D1(Ge_(60.0) N_(40.0)) to the composition point D5(Ge_(45.0)        N_(55.0)),    -   a composition line E1–E5 connecting the composition point        E1(Ge_(50.0) N_(50.0)) to the composition point E5(Ge_(40.0)        N_(60.0)),    -   a composition line F1–F5 connecting the composition point        F1(Ge_(42.9) N_(57.1)) to the composition point F5(Ge_(33.3)        N_(66.7)),    -   a composition line G1–G5 connecting the composition point        G1(Ge_(35.0) N_(65.0)) to the composition point G5(Ge_(30.0)        N_(70.0)),    -   a composition line A1–H2 connecting the composition point        A1(Ge₁₀₀) to the composition point H2(N_(95.0) O_(5.0)),    -   a composition line A1–H3 connecting the composition point        A1(Ge₁₀₀) to the composition point H3(N_(950.0) O_(50.0)), and    -   a composition line A1–H4 connecting the composition point A1        (Ge₁₀₀) to the composition point H4(N_(20.0) O_(80.0)).

That is, preferably the average composition ratio of Ge to N to O in theGe—N—O layer is within the range surrounded by four composition points,that is, B1, B4, G4, G1 in the triangular diagram showing thethree-element composition Ge—N—O shown in FIG. 5. Within this range,there are such an effect that the cycle performance and the erasureperformance can be enhanced as described above.

Similarly to the case of the Ge—N layer, in case of the Ge—N—O layer,when the barrier layer is formed at the side opposite to the substrateof the recording layer (at the side which the laser beam is not incidenton), in the process of recording and erasing, there is less possibilitythat the Ge atom is included in the recording layer. Accordingly, thelayer can be applied to the composition region whose Ge density isconsiderably high. On the contrary, when the barrier layer is formed atthe substrate side of the recording layer (at the side which the laserbeam is incident on), there is more possibility that the Ge atom isincluded in the recording layer. Accordingly, it is not preferable thatthe layer is applied to the composition region whose Ge density isconsiderably high.

Accordingly, even within the composition region B1–B4–G4–G1, when thebarrier layer is formed at the substrate side of the recording layer (atthe side which the laser beam is incident on), the composition regionsurrounded by the four composition points, D1, D4, G4, G1 is preferable.When the barrier layer is formed at the side opposite to the substrateof the recording layer (at the side which the laser beam is not-incidenton), the composition region surrounded the four composition points B1,B4, F4, F1 (preferably, C1, C4, F4, F1) is more preferable.

When the Ge density exceeds the composition line B1–B4, there is morepossibility that the Ge atom is included in the recording layer, therebysometimes the characteristic of the recording layer is changed. On thecontrary, when the Ge density is too less than the composition lineG1–G4, gas-state oxygen and nitrogen included in the film are increased.Accordingly, for example, when a laser-heating is performed, the oxygenand nitrogen is outgassed relative to the interface to the recordinglayer, thereby sometimes there is occurred such a problem that theGe—N—O protective layer is peeled from the recording layer, etc.However, any way, if the Ge—N—O protective layer is formed at least oneside of the recording layer, a predetermined effect can be obtained.

The component ratio of oxygen to nitrogen can be selected according tothe optical constant (refractive index) when the structure of arecording device is determined. For example, in case of Ge₃N₄—GeO₂composition line, the closer a real part n and an imaginary part k ofthe complex refractive index n+ik approach to the Ge₃N₄ side, the largerthey become. The closer the real part n and the imaginary part kapproach to the GeO₂ side, the smaller they become. Accordingly, whenlarger n, k are necessary, the composition containing much nitrogen canbe selected. When smaller n, k are necessary, the composition containingmuch oxygen can be selected.

However, the higher the GeO₂ density becomes, the lower the meltingpoint of the film becomes. When the melting point becomes too low, sincea deformation is occurred due to the repeated laser irradiation, and theprotective layer is mixed with the recording layer, an excessively lowmelting point is not preferable as the protective layer. Furthermore,since GeO₂ itself is subject to melt into water, when GeO₂ densitybecomes higher, there is such a problem that a moisture-proof of theprotective layer is reduced.

In the composition region surrounded by the composition points B1, B4,G4, G1 (in addition to the composition points B1, B4, C1, C4, G4, G1,for example Ge₃₅N₃₀O₃₅, Ge₃₇N₁₈O₄₅, Ge₄₀N₅₅O₅), the good moisture-proofand cycle performance can be confirmed. In view of a repeatingperformance, in the region B1–B3–G3–G1 having a relatively less oxygencomponent (in addition to the composition points B1, B3, G3, G1, forexample Ge₄₀N₄₀O₂₀, Ge₄₂N₅₃O₅, Ge₃₅N₃₅O₃₀, a good repeating performancecan be confirmed.

In the composition whose oxygen density is low, for example, in thecomposition having a less oxygen component than the composition lineA1–H2, the rigidity becomes little larger. Accordingly, compared to thecomposition having more oxygen component, the composition having lessoxygen density has a little tendency to generate the crack and thepeeling. However, a little oxygen is added to the composition havingless oxygen density, thereby such an effect that the peeling and thecrack are prevented can be obtained. As described below, even in thecomposition having less oxygen than the composition line A1–H2, if thethickness of the Ge—N—(O) layer is about 300 nm, there is no practicalproblem. Accordingly, this region can be applied.

When the Ge—N layer or the Ge—N—O layer is applied to the barrier layer,the film thickness thereof is needed to be at least 1 nm or more,preferably 2 nm or more, more preferably 5 nm or more. When the filmthickness is less than 1 nm, such an effect that the diffusion issuppressed is reduced. Furthermore, the difference between 2 nm and 5 nmis an allowance relative to the power. Even if the thickness of 5 nmneeds a higher power than 2 nm, such an effect that the cycleperformance is enhanced can be obtained according to the diffusion andthe chemical reaction. When the film thickness is 5 nm, a basicdiffusion suppression effect can be sufficiently obtained. If thethickness is 20 nm or more, the above effect can be more reproduciblyobtained.

When the Ge—N layer or the Ge—N—O layer is used as the protective layer,it is necessary that the thickness thereof is formed in such a mannerthat it is thicker than thickness of the layer used for the barrierlayer. In case of a usual optical disk, the film thickness of thedielectric protective layer can be only formed in order to have at most300 nm. Accordingly, the thickness of about 300 nm is applied to thefilm thickness of the Ge—N protective layer or the Ge—N—O protectivelayer. In case of Ge—N layer or the Ge—N—O layer, there is no problem,and the crack and the like are not observed. Furthermore, in this pointof view, there is such an advantage that the material system containingoxygen is not subject to crack. It is assumed that oxygen is included,thereby a structure flexibility is enhanced.

Next, a method of preparing the optical information recording mediumwill be explained. The multi-layer film constituting the recordingmedium according to the present invention can be formed by a gas phasedeposition method such as a vacuum deposition method, a DC sputteringmethod, a magnetron sputtering method, a laser sputtering method, an ionplating method, a CVD method and the like. Here, the example using theDC sputtering method and the magnetron sputtering method will bedescribed.

FIG. 6 shows an embodiment of an apparatus for preparing the opticalinformation recording medium. FIG. 6 shows a generally schematicstructure.

In the first place, a vacuum tank 11 of a sputter chamber is a positiveelectrode. The vacuum tank 11 is connected to a plus of a direct currentpower source 13 via a power source switch 12. Furthermore, the vacuumtank 11 is switching-connected to a matching circuit 15 connected to ahigh-frequency power source 14. Thereby, both of the DC sputtering usinga direct current discharge and an RF sputtering using a high-frequencydischarge can be carried out. The matching circuit 15 matches animpedance in the sputter chamber to the impedance at the power source.

A bottom portion of the vacuum tank 11 is provided with four negativeelectrodes 16, 17, 18, 19 (negative electrodes 18, 19 not shown) whichalso serve as a water cooler. An insulating material 44 is disposedaround each negative electrode 16, 17, 18, 19, thereby the negativeelectrodes 16, 17, 18, 19 are insulated from the positive electrode.Furthermore, the negative electrodes 16, 17, 18, 19 can be grounded viaswitches 20, 21, 22, 23 (switches 22 23 not shown).

A Ge—Sb—Te alloy target 45 bonded to a copper backing plate, a ZnS—SiO₂(SiO₂: 20 mol %) mixture target 46, an Al—Cr (Cr: 3 atoms %) alloytarget 47 and a Ge target 48 are fixed to the negative electrodes 16,17, 18, 19 via an O ring by a screw, respectively. Each target isdisc-shaped, having a diameter of 100 mm and a thickness of 6 mm.Furthermore, a permanent magnet (not shown) is accommodated in thenegative electrodes 16, 17, 18, 19, thereby a magnetron discharge can becarried out.

An air outlet 24 is disposed at a side surface the vacuum tank 11. Avacuum pump 26 is connected to the air outlet 24 via a pipe 25, therebyan exhaust can be carried out in such a manner that the sputter chamberis high vacuum. An upper portion of the vacuum tank 11 is provided witha rotating apparatus 27. A disk holder 29 is mounted to a rotary shaft28 of the rotating apparatus 27. The substrate 1 is attached to the diskholder 29. A numeral 30 denotes a shutter. The shutter 30 is closed sothat a pre-sputter is carried out. Furthermore, the shutter 30 is openedand closed, thereby a sputter start and a sputter completion arecontrolled.

One side of a gas pipe 31 for providing a sputter gas is connected tothe vacuum tank 11. The other side of the gas pipe 31 is connected to anAr gas cylinder 40, a Kr gas cylinder 41, an O₂ gas cylinder 42 and anN₂ gas cylinder 43 via a mass flow meters 32, 33, 34, 35 and valves 36,37, 38, 39, respectively. Thereby, aside from the usual sputtering in anAr gas atmosphere, the sputtering in a Kr gas atmosphere, a mixed gas ofAr gas, Kr gas and N₂ gas atmosphere (for example, Ar+N₂), a mixed gasof Ar gas, Kr gas, N₂ gas and O₂ gas atmosphere (for example, Ar⁺ N₂+O₂)can be carried out. The gas containing the nitrogen component is notlimited to the N₂ gas, for example, ammonia, etc. is also included inthe gas containing the nitrogen component. However, considering anapparatus contamination, etc., in general, the N₂ gas is preferable.When the Ge—N—O layer is formed, N₂O, NO, NO₂ or the like is used as thegas containing both of N and O, and the sputtering can be also carriedout in the mixed gas of Ar and them.

The method of preparing the optical information recording medium havingthe structure shown in FIG. 3A as an embodiment of the opticalinformation recording medium according to the present invention by usingthis apparatus will be described below. Here, simultaneously, such anexample that the Ge—N layer or the Ge—N—O layer as the barrier layer isdisposed at the substrate side of the recording layer will be explained(henceforth, in case of no particular explanation, an explanation ismade in an order of Ge—N, Ge—N—O).

In the first place, the vacuum pump 26 is actuated, thereby the vacuumtank is exhausted to a high vacuum of 1×10⁻⁶ Torr or less. Next, a mainvalve is throttled, and at the same time. Ar gas is introduced into thevacuum tank, thereby a degree of vacuum reaches to 1 mTorr. The diskholder 29 is rotated, and the power source switch is turned on, therebyRF discharge is started by the ZnS—SiO₂ target 46 and the negativeelectrode 17. The pre-sputter is carried out with 500 W power for fiveminutes, and after the discharge is stabled, the shutter 30 is opened.After a ZnS—SiO₂ film having a predetermined thickness (according to theembodiment, as described above, 91 nm or 86 nm) is deposited on thesubstrate 1, the shutter 30 is closed. The protective layer 2 comprisingthe ZnS—SiO₂ film is formed on the substrate 1 provided with the groovetrack portion 7.

After the discharge is completed, once the main valve is entirelyopened, the degree of vacuum is returned to 1×10⁻⁶ Torr. Thenceforth,the main valve is throttled again, the Ar gas and the N₂ gas areintroduced at the ratio of 50% to 50%, thereby the total pressure is setto 20 mTorr. Next, the RF discharge is started by the Ge target 48 andthe negative electrode 19. After five-minute pre-sputtering, the shutter30 is opened, and the reactive sputter is carried out with 500 W. Thebarrier layer 8 whose main component is Ge—N having a predeterminedthickness (according to the embodiment, as described above, 5 nm or 20nm) is formed on the previously formed ZnS—SiO₂ protective layer 2(since the opening and closing operation of the shutter 30 and the valveoperation are similar to the case of forming the following layers, theexplanation is omitted). When the barrier layer whose main component isGe—N—O is formed, in the above process, instead of introducing the Argas and the N₂ gas at the ratio of 50% to 50%, the Ar gas, the N₂ gasand the O₂ gas can be only introduced at the pressure ratio of 49.5% to49.5% to 1%. Only this point is different from the above case.Similarly, the succeeding process is carried out.

Since Ge has more tendency to form the oxide rather than the nitride,for example, the O₂ density can be set considerably less than the N₂density. In some cases, the mixed gas of the Ar gas and the gascontaining an N component can be only used as an introducing gas,thereby the Ge—N film containing oxygen, that is, the Ge—N—O layer canbe formed. In this case, such an administration that the degree ofvacuum is set within a predetermined range before introducing the gas,etc. is carried out, thereby the O density in the Ge—N—O layer can becontrolled in such a manner that a desired O density is obtained.

The composition of the Ge—N layer and the Ge—N—O layer can be identifiedby a combination of an auger electron spectral method (AES), aRuthurford back scattering method (RBS), an Inductive Combinationhigh-frequency plasma spectral method (ICP), and the like. Thecompositions in this case are Ge₄₄N₅₆, Ge₄₀N₄₀O₂₀, respectively.

Next, DC discharge is started by the Ge—Sb—Te target 45 and the negativeelectrode 16, thereby the recording layer 3 is formed. The Ar gas isintroduced so that the degree of vacuum is set to 0.5 mTorr. Thesputtering is carried out with 100 W power in such a manner that apredetermined film thickness (according to the embodiment, as describedabove, 20 nm) can be obtained. The formed recording layer 3 is inamorphous state.

Next, the ZnS—SiO₂ film of the upper protective layer 4 is formed underthe same condition as the lower protective layer 2 of a first layer insuch a manner that a predetermined film thickness (according to theembodiment, as described above; 18 nm) can be obtained. Finally, theAl—Cr target 47 is DC sputtered in the Ar gas atmosphere of 2 mTorr with300 W power. The Al—Cr alloy film of the metallic reflecting layer 5 isalso deposited at a predetermined thickness (according to theembodiment, as described above, 150 nm), thereby the multi-layer filmhaving a predetermined five-layer structure is formed on the substrate1.

The formed medium is taken out the vacuum tank 11, and the metallicreflecting layer 5 is covered with the ultraviolet curing resin. Thedummy substrate is laminated on the covered metallic reflecting layer 5so carefully not as to generate a bubble. In this state, the ultravioletis irradiated, and a coated layer of the ultraviolet curing resin iscured, thereby an adhesive structure provided with a contact layer 9 anda protective defense plate 10.

According to the above example, as the method of forming the Ge—N layeror the Ge—N—O layer, the metal Ge is used as the target, and the mixedgas of the Ar gas and the nitrogen gas or the mixed gas of the Ar gas,the nitrogen gas and the oxygen gas are used so that the film is formedby the reactive sputtering method. However, there are other methods.

Other methods are as follows. Instead of the metal Ge, a Ge—N compound(preferably, Ge₃N₄) is used as the target. The reactive sputtering iscarried out in the mixed gas containing the rare gas and the nitrogen sothat the film is prepared. Furthermore, a Ge—O compound (preferably,GeO, GeO₂) is used as the target. The reactive sputtering is carried outin the mixed gas of the rare gas and the nitrogen, or in the mixed gasof the rare gas, the nitrogen-containing gas and the oxygen-containinggas so that the film is prepared. Furthermore, a Ge—N—O compound (forexample, the compound of Ge₃N₄ and GeO₂ or GeO) is used as the target.The reactive sputtering is carried out in the mixed gas of the rare gasand the nitrogen-containing gas, or in the mixed gas of the rare gas,the nitrogen-containing gas and the oxygen-containing gas so that thefilm is formed.

When the film is formed, in case that impurities such as Ar, H, Si, C,etc. contained in the sputter gas and the chamber are contained in thebarrier layer 8, if the impurity density is 10 at % or less, the similareffect to the case that the impurity is not contained can be obtained.That is, preferably, the impurity density contained in the nitride andthe oxide forming the barrier layer 8 is about 10 at % or less. In caseof an admixture for positively enhancing the characteristic, the densityis not limited to this range. For example, Cr can be added up to thesame density as the Ge density at maximum, thereby Cr largelycontributes to enhancing the adhesiveness to the recording layer, etc.

As a second method of forming the barrier layer, for example, thematerial of the recording layer is applied to the target, and thenitride and nitriding-oxide being the constituent elements of therecording layer are formed, thereby the barrier layer can be formed. Forexample, in case of a Ge—Sb—Te system recording layer, the Ge—Te—Sballoy target is used so that Ge—Sb—Te—N and Ge—Sb—Te—N—O can be formed.In case of this method, for example, in the first place, after theprotective layer is formed, the Ge—Sb—Te target is used, and thereactive sputtering is carried out in the mixed gas of Ar+ N₂ therebythe Ge—Sb—Te—N film is formed in order to have a predeterminedthickness. After then, Ar is used as the sputter gas, and the Ge—Sb—Terecording layer is formed. By this process, only one target is used,thereby the barrier layer and the recording layer can be formed.

According to the embodiment, such an example that the process of formingthe recording layer is performed in inactive gas is shown. The nitrogencan be contained in the recording layer. In this case, the N₂ partialpressure is appropriately adjusted. In case of forming the recordinglayer, compared to the case of forming the barrier layer, a low N₂density is selected, thereby the recording layer containing the nitrogenand the barrier layer can be laminated. Here, the example of preparingthe optical information recording medium having the structure shown inFIG. 3A is shown. For example, as shown in FIG. 3F, in case of thestructure having the protective layers comprising the barrier materialat both sides of the recording layer 3, the protective layer comprisingthe nitride and nitriding-oxide, the recording layer and the protectivelayer comprising the nitride and nitriding-oxide can be formed accordingto the above process.

Furthermore, for example, as shown in FIG. 3E, when the protective layercomprising the barrier material is formed on only the upper surface ofthe recording layer 3, naturally, the films can be formed in the orderof the recording layer, the protective layer comprising the nitride andnitriding-oxide. In case of this method, since the composition of therecording layer is common to that of the barrier layer or the protectivelayer, there is less fear that the chemical reaction and theinterdiffusion are occurred. Accordingly, a higher adhesiveness can beeasily obtained. Extending this view, for example, when the Ge—Sb—Terecording layer is used, it is advantageous that the constituentelements of the Ge—Sb—Te recording layer, that is, the nitride andnitriding-oxide such as Te and Sb are used as the barrier layer and theprotective layer themselves. In this case, the metal Te and the metal Sbare used as the target, and Te—N, Te—N—O and Sb—N, Sb—N—O can beselectively independently formed, respectively. In any case, the effectcorresponding to the Ge—N—O layer can be obtained. In case of thebarrier layer and the protective layer using the nitride and thenitriding-oxide, for example, as shown by the case of Ge—N—O, thecomposition ratio of the nitrogen element, the oxygen element and themetal element is not limited to the stoichiometric composition.

According to the present invention, when a heat is applied, in theconstituent element of the recording layer and/or the constituentelement of the dielectric material layer, a material movement issuppressed. The layer having a higher adhesiveness to the recordinglayer and/or the dielectric material layer is adhesively formed on atleast one surface of the recording layer. If this requirement can beonly satisfied, the constituent element of the recording layer is notlimited to nitriding-oxide. Accordingly, even if the constituent elementof the recording layer is a carbide or a fluoride, the constituentelement can be applied. For example, the constituent element of therecording layer may be the same as the constituent element (for example,Zn—N, Zn—N—O, etc.) of the dielectric protective layer. Furthermore, itis expected that the mixture of the compound except for nitriding-oxidecan be applied. Even if In—Sb—Te and Ag—In—Sb—Te systems etc. which donot contain Ge are used as the recording material, the Ge—N film and theGe—N—O film are effective.

Next, the formed recording medium is initialized. The initialization iscarried out by the laser irradiation, as described below. Any othermethod, for example, the method using a flush exposure can be applied.Here, the disk medium is rotated at linear rate of 5 m/s at uniformrate, and the laser beam having a wavelength of 780 nm is formed in sucha manner that an oblong spot of 1 μm×100 μm (a half value width) isformed on the disk. The disk medium is located in such a manner that thelongitudinal direction of the oblong spot thereof is a radius direction.The crystallization is sequentially carried out at a pitch of 30μm/rotation from an outer diameter to an inner diameter.

Thereby, the method of preparing the optical information recordingmedium according to one embodiment of the present invention is shown. Ifthe number of layers and the layer thickness of the disk are changed,the above method is substantially similar. Furthermore, the mediumhaving various structures as shown in FIGS. 3A to 3H and FIGS. 4A to 4Hcan be similarly formed.

Furthermore, a disk comprising a plurality of laminated recording layersin which a multi-layer recording can be carried out, and a diskcomprising two laminated disks with rear surfaces thereof in which therecord can be reproduced at both sides can be applied to the presentinvention.

Next, the signal is recorded on the optical information medium preparedby the above method, and the method of reproducing the record will beexplained. In order to estimate the recording and reproducingcharacteristic, a deck is used. The deck is provided with asemiconductor laser light source whose wavelength is 680 nm, an opticalhead mounting an objective lens whose numerical aperture is 0.6, alinear motor for guiding the optical head to an optional position of therecording medium, a tracking servo mechanism for controlling apositioning, a circuit for the tracking servo mechanism, a focusingservo mechanism for controlling an attitude of the optical head and forirradiating a recording film surface with a laser spot, a circuit forthe focusing servo mechanism, a laser drive circuit for modulating apower of the laser, a time interval analyzer for measuring a jittervalue of the reproduced signal, and a rotation control mechanism forrotating the optical disk.

When the signal is recorded or overwritten, in the first place, the diskis rotated at a predetermined rate. The linear motor is operated so thatthe optical head is moved to the optional track position. Next, thefocusing servo mechanism is operated so that the laser spot is focusedon the recording film surface. Next, the tracking servo mechanism isoperated so that the laser beam is tracked to an optional track. Next,the laser drive circuit is operated so that the power of the outputtedlaser is modulated corresponding to the information signal between anamorphizing pulse portion having a power level whose irradiation energyis relatively high and a crystallizing pulse portion having a powerlevel whose irradiation energy is relatively low, as shown in FIG. 7.The optical information recording medium is irradiated with the laserbeam, thereby such a state that an amorphous state and a crystallinestate alternately exist is formed.

A peak pulse portion comprises a usually so-called multi-path formed byfurther narrow pulse sequence. After the irradiated portion in theamorphizing pulse portion is melted in an instant, the portion isquenched, thereby the portion is in the amorphous state. The irradiatedportion in the crystallizing pulse portion is annealed, thereby theportion is in the crystalline state.

Next, when the signal is reproduced, the irradiation power of the laserbeam is set to a reproducing power level lower than the power level usedfor the crystallization in such a manner that the optical informationrecording medium is not further changed. The optically changed portionis irradiated with the laser beam, and a detector receives and detects astrength change generated corresponding to a difference between theamorphous state and the crystalline state of the reflecting light or thetransmitted light.

A pulse waveform is not limited to the waveform shown in FIG. 7. Forexample, as shown in FIG. 8, (A) the amorphizing pulse is modulatedbetween the amorphizing power level and the level less than thereproducing power level, (B) only pulse widths of a top pulse and a tailpulse are relatively longer than the pulse width of a intermediatepulse, (C) the amorphizing pulse width makes equal, (D) when the laserbeam is amorphized, without a pulse modulation, the beam is irradiated,(E) such a period that the pulse has the power level less than thereproducing power level is necessarily provided before and/or after theamorphizing pulse, or the waveforms as shown in (A) to (E) are combinedto one another, etc. Thereby, various recording systems, reproducingsystems and erasure systems can be applied.

A signal system is EFM, a shortest recording mark length is 0.61 μm, anda shortest bit length is 0.41 μm. The disk is fixed to a turn table, andit is rotated at 2045 rpm. At the position whose recording radius is 28mm (linear rate 6 m/s), the overwrite of a random signal for recording amark length within the range from 3T to 11T on the groove track isrepeated. The change of the signal amplitude and the jitter value (theratio (σ sum/Tw) of σ sum, that is, a sum of a standard deviation σ ofthe jitter value of each signal mark 3T–11T to a window width Tw(=34ns), the jitter value can be only 12.8% or less) is examined.

For a comparison, three kinds of disks (A), (B), (C) are made on anexperimental basis and estimated. The disks are as follows: (A) twodisks comprising the structure according to the embodiment (a disk A1 isa Ge—N barrier layer disk, a disk A2 is a Ge—N—O barrier layer disk),(B) a disk comprising a conventional structure, that is, the structureof the disk (A) except for the Ge—N barrier layer or the Ge—N—O barrierlayer, and (C) a disk comprising the conventional structure in which anSi₃N₄ interface layer is formed instead of the Ge—N barrier layer or theGe—N—O barrier layer of the disk (A) according to the embodiment.

According to a first estimate item, after the record is repeated at100,000 times, the jitter value (measured by such a method that thejitter between each mark front end and the jitter between each mark rearend are independently measured) is estimated. Such a case that both ofthe jitter between the mark front end and the front end and the jitterbetween the mark rear end and the rear end are less than a referencevalue and the jitter value is scarcely changed is represented by ⊚. Sucha case that although the jitter value is changed, the jitter valueitself remains less than the reference value is represented by ∘. Such acase that after 100,000-time repeating, the jitter slightly exceeds thereference value is represented by Δ. Such a case that after 10,000-timerepeating, the jitter value already exceeds the reference value isrepresented by X. The power for estimate is set to a higher value byabout 10% than a lowest limit jitter value, where the lowest limitjitter value denotes the value when an initial jitter value satisfiesthe value less than 12.8%.

According to a second estimate item, after 100,000-time repeating in theabove experimental track, the amplitude value is observed, and theresult is estimated. Such a case that less change is found isrepresented by ⊚. Such a case that about 10% change is found isrepresented by ∘. Such a case that about 20% change is found isrepresented by Δ. Such a case that the amplitude value is reduced tomore than 20% is represented by X.

A third estimate item is a weather-proof After the disks are left tostand under a high-temperature (90° C.) and high-humidity (80% RH)environment for 200 hours and for 400 hours, the disks are examined witha microscope. Such a case that no change is found even after 400 hoursis represented by ⊚. Such a case that a slight peeling, etc. is foundafter 200 hours is represented by ∘. Such a case that a slight peelingis observed in 200 hours is represented by Δ. Such a case that a largepeeling is observed within 200 hours is represented by X.

The above experimental results are shown in Table 2. Thus, the structureaccording to the present invention is superior to the conventionalstructure in view of the repeating characteristic and the weatherproof.

TABLE 2 Result 1 of comparing the characteristics of the optical diskapplying the barrier layer according to the present invention to thoseof the prior art Estimate Items Signal Weather-proof Disk JitterAmplitude (Peeling, etc.) A1 ⊚ ⊚ ⊚ A2 ⊚ ⊚ ⊚ B Δ Δ ⊚ C ◯ ◯ X

Next, in order that the effect of the barrier layer relative to theerasure performance is confirmed, the result of a comparative test isshown. A disk (D) comprising the structure shown in FIG. 3B in which thebarrier layer is used only at the reflecting layer side of the recordinglayer in Table 1, and a disk (E) comprising the structure shown in FIG.3C in which the barrier layer is used at both sides of the recordinglayer are produced by the above method. The disks (D) and (E) areinitialized. The composition of the reflecting layer and the recordinglayer is same as that of the disks (A) and (B).

The disks (D1) and (D2) comprise a laminated-layer structure, in which aZnS—SiO₂ protective layer (86 nm), a Ge—Sb—Te recording layer (20 nm), aGe—N or Ge—N—O barrier layer (5 nm), a ZnS—SiO₂ protective layer (18 nm)and an Al—Cr reflecting layer (150 nm) on the substrate. The disks (E1)and (E2) comprise a laminated-layer structure, in which a ZnS—SiO₂protective layer (86 nm), a Ge—N or Ge—N-0 barrier layer (5 nm), aGe—Sb—Te recording layer (20 nm), a Ge—N or Ge—N—O barrier layer (5 nm),a ZnS—SiO₂ protective layer (12 nm), and an Al—Cr reflecting layer (150nm).

Here, when the Ge—N layer or the Ge—N—O layer is formed at thereflecting layer side of the recording layer, compared to the case thatthe Ge—N layer or the Ge—N—O layer is formed at the substrate side, thepressure ratio of the N₂ gas relative to Ar gas is reduced. The gas isintroduced at the ratio of 80% Ar gas to 20% N₂ gas, or in the ratio of80% Ar gas to 19.5% N₂ gas to 0.5% O₂ gas. The sputtering is carried outat the total pressure of 20 mTorr. As a result, the average compositionof the Ge—N layer at the reflecting layer side is Ge₆₅N₃₅, and thecomposition of the Ge—N—O layer at the reflecting layer side isGe₆₀N₃₀O₁₀.

The disks (A) to (E) are rotated at the linear rate 6 m/s, and theresult is recorded according to the above method. Here, a single signalhaving a 3T mark length is recorded. And after C/N ratio is measured,immediately the overwrite of a 11T signal is recorded. Thereby the 3Tsignal is erased, and a damping factor ratio (a degree of erasure) ismeasured. Next, after another signal is recorded, the disks are left tostand in a dryer at 90° C., the overwrite of the 11T signal is recorded,and the degree of erasure is measured. The leaving time is twoconditions, that is, 100 hours and 200 hours. The result is shown inTable 3.

In Table 3, ⊚ denotes that a sufficiently high erasure ratio more than35 dB is obtained. ∘ denotes that the erasure ratio more than 30 dB isobtained. Δ denotes that the erasure ratio more than 26 dB is obtained.X denotes that the erasure ratio is reduced to less than 26 dB. Thereby,the Ge—N barrier layer or the Ge—N—O barrier layer is applied, therebythe erasure performance is enhanced. More specifically, when the barrierlayer is formed at the reflecting layer side of the recording layer, ahigher effect can be obtained.

TABLE 3 Result 2 of comparing the characteristics of the optical diskapplying the interface layer according to the present invention to thoseof the prior art Estimate Items Immediately Disk After 100 H 200 H A1 ⊚◯ Δ A2 ⊚ ◯ Δ B ⊚ Δ X C ⊚ Δ X D1 ⊚ ⊚ ◯ D2 ⊚ ⊚ ◯ E1 ⊚ ⊚ ⊚ E2 ⊚ ⊚ ⊚

Henceforth, according to more detailed experimental data, the presentinvention will be explained in detail. FIG. 9 schematically shows a filmformation apparatus used for the following experiment. A vacuum pump(not shown) is connected to a vacuum container 49 through an air outlet50 so that a high vacuum can be kept in the vacuum container 49. From agas supplying opening 51, the Ar gas, the nitrogen gas, the oxygen gasor the mixed gas of them can be appropriately provided at a constantflow rate on demand. A numeral 52 denotes a substrate. The substrate 52is mounted to a drive apparatus 53 for rotating the substrate 52. Anumeral 54 denotes a sputter target. The sputter target 54 is connectedto a negative electrode 55. Here, a disc-shaped material having adiameter of 10 cm and a thickness of 6 mm is used as the target. Thenegative electrode 55 is connected to a direct current power source or ahigh-frequency power source through a switch (not shown). Furthermore,the vacuum container 49 is grounded, thereby the vacuum container 49 andthe substrate 52 are kept a positive electrode.

FIG. 17 shows an exemplary structure of a layer of an opticalinformation recording medium of the present invention. This opticalinformation recording medium includes a protective layer 62, a firstdiffusion preventing layer (Ge-containing layer) 67, a recording layer63, a second diffusion preventing layer (Ge-containing layer) 68, and areflection layer 65, which are laminated on a substrate 61 in thisorder.

Optical information can be recorded, erased and reproduced on therecording layer 63.

The diffusion preventing layer is preferably formed on at least onesurface of the recording layer 63. The diffusion preventing layers 67and 68 are formed for the purpose of preventing atoms from diffusingbetween the recording layer 63 and layers adjacent to the recordinglayer 63. When the protective layer comprises sulfur or a sulfide, thediffusion preventing layer is particularly effective to prevent thesecomponents from diffusing. Although the diffusion preventing layer canbe formed on either one surface or both faces of the recording layer 63,it is preferable to form on both faces of the recording layer in orderto prevent atoms from diffusing between the layers more effectively, asshown in FIG. 17. When the diffusion preventing layer is formed on onlyone surface of the recording layer, it is preferable to form thediffusion preventing layer on the side that has a larger load of heat atthe recording layer interface, namely, on the side where thetemperature-rise at the recording layer interface at the time of markingand erasing is large. This is generally the side the laser beams strike.

The components included in the diffusion preventing layer may diffuse tothe recording layer after recording information repeatedly. However, theselection of a suitable composition of a material for the diffusionpreventing layer that hardly interferes with a change in the opticalcharacteristics of the recording layer can prevent a harm caused by suchdiffusion.

In this embodiment, the diffusion preventing layers 67 and 68 are mainlycomposed of GeXN or GeXON, where X represents at least one elementselected from the group consisting of elements belonging to Groups IIIa,IVa, Va, VIIa, VIIa, VIII, Ib and IIb, and C. X is not particularlylimited, but X is preferably at least one element selected from thegroup consisting of Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Pd, Ag, Cd, Hf,Ta, W, Fe, Co, Ni, Y, La and Au, more preferably at least one elementselected from the group consisting of Cr, Mo, Mn, Ti, Zr, Nb, Ta, Fe,Co, Ni, Y and La, and further more preferably at least one elementselected from the group consisting of Cr, Mo, Mn, Ni, Co and La.

The reason why the addition of X improves the durability of the mediumis believed to be that the added X suppresses the introduction ofmoisture into the diffusion preventing layer, although this is notfirmly confirmed. A possible mechanism is as follows. In a GeN or GeONlayer, Ge—N bonds change to Ge—O or Ge—OH bonds under the conditions ofhigh temperature and high humidity and are ready to corrode. When X thatis oxidized relatively easily is added to the layer, the phenomenon ofoxidation or hydration of Ge is suppressed. It is also possible that theproduction of dangling bonds of Ge present in a GeN or GeON layer issuppressed by the addition of X, and thus the formation of Ge—OH bondsis suppressed. It is believed that this is the reason why preferableexamples of X are Cr, Mo, Mn, Ti, Zr, Nb, Ta, Fe, Co, Ni, Y and La(further more preferably Cr, Mo, Mn, Ni, Co and La).

These diffusion preventing layers 67 and 68 differ from conventionallayers including a nitride such as boron nitride, aluminum nitride,silicon nitride or the like, in that the diffusion preventing layers 67and 68 comprise a nitride or a nitrogen oxide of germanium as the basiccomponent. The conventionally used nitride provides poor adhesivenessbetween the diffusion preventing layer and the recording layer or thesubstrate due to the internal stress, the slip property or the like. Onthe other hand, germanium nitride or germanium nitrogen oxide providesgood adhesiveness with the recording layer or the like and has an effectof suppressing the movement of elements. The addition of theabove-described X to such germanium nitride (nitrogen oxide) providesthe diffusion preventing layers 67 and 68 with better durability andcharacteristics in repetitive recording.

However, the optical information recording medium is not limited to thestructure as described above but can have other structures. For example,the protective layer 62 can be formed of the material of the diffusionpreventing layer 67; a layer formed of another material (e.g., asemiconductor such as Si or Ge, a metal such as Cr, Mo or Nb, a varietyof dielectrics, combinations thereof or the like) can be formed betweenthe diffusion preventing layer 68 and the reflection layer 65; adielectric layer can be formed in a relatively large thickness betweenthe diffusion preventing layer 68 and the reflection layer 65, which isa so-called annealing structure; a reflection layer need not to beformed; the reflection layer can be composed of two layers; or anotherfilm made of another material can be formed between the substrate 61 andthe protective layer 62. Any of these structures and others can make useof the present invention.

The substrate 61 is preferably formed of a resin such as polycarbonate,PMMA or glass and preferably includes a guiding groove for guiding laserbeams.

The protective layer 62 is formed for the purpose of protecting therecording layer, improving the adhesiveness with the substrate,adjusting the optical characteristics of the medium or the like. Theprotective layer 62 is preferably formed of a dielectric such as asulfide such as ZnS, an oxide such as SiO₂, Ta₂O₅ or Al₂O₃, a nitridesuch as Ge₃N₄, Si₃N₄ or AlN, a nitrogen oxide such as GeON, SiON orAlON, a carbide, a fluoride or the like, or combinations thereof (e.g.,ZnS—SiO₀).

The reflection layer 65 is preferably formed of a metal such as Au, Al,Cr, Ni or the like, or an alloy of metals suitably selected from thesemetals.

The recording layer 63 is preferably formed of a phase-changeablematerial such as a Ge—Sb—Te based material, a Te—Sn—Ge based material, aTe—Sb—Ge—Se based material, a Te—Sn—Ge—Au based material, an Ag—In—Sb—Tebased material, an In—Sb—Se based material, an In—Te—Se based material,more specifically, an alloy of each material. The recording layer 63 ispreferably formed of a phase-changeable material comprising Te, Se or Sbas the main component, and more preferably a phase-changeable materialcomprising three elements of Ge, Te and Sb as the main component.

The thickness of the recording layer 63 is preferably in the range from5 nm to 25 nm. When the thickness is less than 5 nm, the recordingmaterial is hardly formed into a layer. When the thickness is more than25 nm, heat transfer becomes large in the recording layer, so thaterasion is likely to occur in adjacent portions during high-densityrecording.

The recording layer 63 may comprise impurities such as sputteringcomponents such as Ar, Kr, or the like, or H, C, H₂O or the like, but itdoes not matter even if impurities are included, as long as the objectof the present invention can be achieved. Furthermore, the diffusionpreventing layers 67 and 68 and the protective layer 62 may compriseimpurities such as sputtering components such as Ar, Kr, or the like, orH, C, H₂O or the like, as in the case of the recording layer 63, but itdoes not matter even if impurities are included, as long as the objectof the present invention can be achieved.

Hereinafter, the diffusion preventing layers 67 and 68 will be detailed.

The composition of the diffusion preventing layer is preferablyrepresented by (Ge_(1-y)X_(y))_(g)O_(h)N_(i), where g>0, h≧0, i>0, andg+h+i=100; and y is a value larger than 0 and smaller than 1, preferably0.5 or smaller for the reason discussed later.

In order to reduce excess atoms, the composition ratio of (GeX), O and Nin the diffusion preventing layers 67 and 68 preferably has numericalvalues which lie within the range represented by the area ABDC in theternary phase diagram of (Ge X), O and N of FIG. 18, where the points A,B, C and D are as follows:

-   -   A ((GeX)_(90.0)O_(0.0)N_(10.0)), B        ((GeX)_(83.4)O_(13.3)N_(3.3)),    -   C ((GeX)_(35.0)O_(0.0)N_(65.0)), D        ((GeX)_(31.1)O_(55.1)N_(13.8)), and more        preferably the area EFDC in the ternary phase diagram of FIG.        18, where additional points E and F are as follows:    -   E ((GeX)_(65.0)O_(0.0)N_(35.0)), F        ((GeX)_(53.9)O_(9.20)N_(36.9)), where (GeX) represents the total        amount of Ge and X.

Since the diffusion preventing layer is susceptible to heat load duringrepetitive recording, the composition ratio in this layer is preferablywithin the range represented by the area EFDC (in order words, astoichiometric composition in the vicinity of Ge₃N₄—GeO₂ line in theternary phase diagram). On the other hand, it is preferable not tocomprise excess N or O in the composition ratio of the diffusionpreventing layer 68 in view of the adhesiveness with the recordinglayer. Therefore, the composition ratio is preferably slightly on theside of the apex of GeX than the Ge₃N₄—GeO₂ line.

When Ge or X that is not bonded to nitrogen or oxygen is presentexcessively, the excess Ge or X diffuses to the recording layer. Thismay interfere with the change in the optical characteristics of therecording layer.

On the other hand, if nitrogen or oxygen that is not bonded to Ge or Xis present excessively, the excess atoms of nitrogen and oxygen floodinto the recording layer. This may interfere with recording. Therefore,the diffusion preventing layers 7 and 8 preferably have (GeX) at such acomposition ratio that X is 50 atom % or less (i.e., 0<y≦0.5 inGe_(1-y)X_(y)). When the content of X is more than 50 atom % of thecontent of GeX, the substance X floods into the recording layer afterrepeated recording, and this tends to interfere with the change in theoptical characteristics of the recording layer. For the same reason, thecontent of X is more preferably 40 atom % or less of the content of GeX,and most preferably 30 atom % or less. On the other hand, the content ofX is preferably 10 atom % or more of the content of GeX. The content ofX of less than 10 atom % may not provide as useful an effect from theaddition of the substance X.

The thickness of the diffusion preventing layer is preferably 1 nm ormore. The thickness of less than 1 nm reduces the effect as thediffusion preventing layer. The upper limit of the thickness of thediffusion preventing layer, for example the diffusion preventing layeron the side closer to irradiation of laser beams than the recordinglayer, is in the range where a sufficient intensity of laser beams so asto record information in or reproduce information from the recordinglayer can be obtained. The intensity of the laser beams can be suitablyset depending on the laser power or the material used for the recordinglayer.

In the case where the diffusion preventing layers are formed in contactwith both faces of the recording layer, it is preferable to usediffusion preventing layers having different compositions. For example,since the layer on the surface on which laser beams are incident issusceptible to the load of heat during repetitive recording, the layerpreferably has a smaller content of X than the layer on the oppositesurface. Furthermore, the layer formed immediately after the formationof the recording layer has a lower adhesiveness than the layer formedimmediately before the formation of the recording layer. Therefore, itis preferable that the diffusion preventing layer formed immediatelyafter the formation of the recording layer has a larger content of Xthan the layer formed immediately before the formation of the recordinglayer. Therefore, in the case where the diffusion preventing layer onthe surface on which laser beams are incident has a compositionrepresented by (Ge_(1-m)X_(m))_(a)O_(b)N_(c) (a>0, b≧0, c>0, 0<m<1,preferably 0<m≦0.5), and the diffusion preventing layer on the oppositesurface has a composition represented by (Ge_(1-n)X_(n))_(d)O_(e)N_(f)(d>0, e≧0, f>0, 0<n<1, preferably 0<n≦0.5), m is preferably smaller thann. In the case where the diffusion preventing layer is formed in contactwith the substrate, in order to improve adhesiveness between thesubstrate and the diffusion preventing film, it is preferable to formthe diffusion preventing layer of a material comprising oxygen or toincrease the content of oxygen at the interface between the diffusionpreventing layer and the substrate.

Next, a method for producing the optical information recording medium ofthe present invention will be described. A multilayer structure formingthe optical information recording medium can be produced by sputtering,a vacuum evaporation method, a chemical vapor deposition (CVD) method orthe like. In this embodiment, sputtering is used. FIG. 19 is a schematicview showing an exemplary film-forming apparatus.

A vacuum pump (not shown) is connected to a vacuum container 69 throughan air outlet 75 so that a high degree of vacuum can be maintained inthe vacuum container 69. A constant flow rate of Ar, nitrogen, oxygen ora mixed gas thereof can be supplied from a gas supply inlet 74. Asubstrate 70 is attached to a driving apparatus 71 for revolving thesubstrate 70. Each sputtering target 72 is connected to a cathode 73.The shape of the target is, for example, a disk having a diameter ofabout 10 cm and a thickness of about 6 mm. The cathode 73 is connectedto a direct current power source or a high frequency power source (notshown) through a switch. Furthermore, the vacuum container 69 isgrounded so that the vacuum container 69 and the substrate 70 areutilized as anodes.

In the process for producing the optical information recording mediumperformed by using such an apparatus, a diffusion preventing layer isformed before and/or after a process for forming a recording layer.

As a target for forming the recording layer 63, for example, a GeTeSbtarget can be used.

When the diffusion preventing layers 67 and 68 are formed by reactivesputtering, a film with good quality can be obtained. It is preferableto use an alloy of Ge and X or a mixture of Ge and X. Moreover, nitrogencan be included in the target. For example, in the case where GeCrN isformed as a diffusion preventing layer, a GeCr target or a GeCr targetfurther provided with N can be used. Furthermore, it is preferable touse a mixed gas of rare gas and nitrogen (N₂) as a film-forming gas. Amixed gas of rare gas and gas containing nitrogen atoms such as N₂O,NO₂, NO, N₂ or a mixture thereof can be used as a film-forming gas.Furthermore, in order to avoid a rigid film or a film having a largestress, it is preferable to add a trace of oxygen to the film-forminggas. A film with good quality may be obtained. The total pressure of thefilm-forming gas is preferably 1.0 mTorr or more.

Furthermore, the partial pressure of nitrogen is preferably 10% or moreof the total pressure of the film-forming gas, because an excessivelylow partial pressure makes it difficult to form a nitride and thusdifficult to form a nitride having a desired composition. A preferableupper limit of the partial pressure is in the range that provides stabledischarge, for example, about 60%.

Next, a method for reproducing and erasing information recorded in thethus obtained optical information recording medium of the presentinvention will be described.

For reproducing and erasing signals, a semiconductor laser light source,an optical head including an object lens, a driving apparatus forguiding laser beams to a predetermined position for irradiation, atracking control apparatus and a focusing control apparatus forcontrolling a position orthogonal to a track direction and a surface ofa film, a laser driving apparatus for adjusting laser power, and arotation control apparatus for rotating the medium are used. Theseapparatuses are conventionally used by those skilled in the art.

For recording and erasing signals, laser beams are focused on amicrospot by an optical system, and the medium rotated by the rotationcontrol apparatus is irradiated with the laser beams. Herein, a powerlevel for the formation of an amorphous state that allows a portion inthe recording layer to reversibly change to an amorphous state byirradiation of laser beams is represented by P₁. A power level for theformation of a crystalline state that allows a portion in the recordinglayer to reversibly change to a crystalline state by irradiation oflaser beams is represented by P₂. By adjusting the power of theirradiated laser beams between P₁ and P₂, marks are recorded or erasedportions are formed, and recording, erasing or overwriting informationcan be performed selectively. In this embodiment, a so-called multiplepulse, where pulse trains are formed in a portion irradiated with laserbeams having a power level of P₁, is formed. However, other types ofpulse than the multiple pulse can be used.

On the other hand, signals from the medium obtained by irradiating themedium with laser beams having a power level P₃ are read by a detectorso as to reproduce the information signals. Herein, P₃ is a reproductionpower level lower than the power levels P₁ and P₂, and the irradiationof laser beams having P₃ does not influence the optical state of therecorded marks and provides a sufficient reflectance so as to reproducethe recorded marks from the medium.

Examples of the conditions are as follows: the wavelength of the laserbeams is 650 nm; the numerical aperture of the used object lens is 0.60;the signal system is an EFM modulation system; the minimum bit length is0.41 μm; the scanning speed of the laser beams in the track direction is6 m/s; the track pitch is 1.48 μm, i.e., a groove and a land (a portionbetween grooves) are alternately formed at every 0.74 μm on a substrate.However, a substrate may include grooves and lands formed at a differentwidth ratio.

In the method for using the optical information recording medium, theconditions are not limited to those described above.

Furthermore, it is preferable to perform so-called “land-grooverecording” where recording, reproducing and erasing information signalsare performed in both the groove portion and the land portion in aguiding groove, because this allows a medium to have a large capacity.In this case, it is necessary to form a suitable depth and shape of theguiding groove and a structure having a suitable reflectance of themedium so that cross-talk or cross-erase does not occur.

EXAMPLE 1

The optical disks having the layer structure shown in FIGS. 3A and 3B (adisk (1) and a disk (3) in a table 4) are made on a experimental basis.The recording layer 3 comprises a phase change material whose maincomponent is a Ge2Sb2.3Te5 alloy, and the dielectric protective layers 2and 4 comprises a ZnS—SiO₂ film. When the film is formed, the gas issupplied in such a manner that each total pressure of the Ar gas becomes1.0 mTorr and 0.5 mTorr, respectively, and each of the powers DC1.27W/cm² and RF6.37 W/cm² is introduced into the negative electrode 55,respectively. Furthermore, when the reflecting layer (AlCr) 5 is formed,the Ar gas is supplied in such a manner that the total pressure becomes3.0 mTorr, thereby the power DC 4.45 W/cm² is introduced.

In the disk (1), after the dielectric protective layer is formed,sequentially, the barrier layer 8 is formed. In the disk (3), after therecording layer 3 is formed, sequentially, the barrier layer 8 isformed. In this case, Ge is used as the target, and the mixture of Arand nitrogen is used as the sputter gas. Furthermore, the sputter gaspressure is 20 mTorr, the partial pressure ratio of Ar to nitrogen inthe sputter gas is 2:1, and the sputter power is RF700 W. Since thetarget is a disc whose diameter is 10 cm, converted into a sputter powerdensity, the sputter power density is 6.37 W/cm².

The film thickness of each layer is as follows: the disk (1) comprisesthe dielectric protective layer 2 having 86 nm, the barrier layer 8having 5 nm, the recording layer 3 having 20 nm, the dielectricprotective layer 4 having 17.7 nm and the reflecting layer 5 having 150nm, and the disk (3) comprises the dielectric protective layer 2 having91 nm, the recording layer 3 having 20 nm, the barrier layer 8 having 10nm, the dielectric protective layer 4 having 15.2 nm and the reflectinglayer 5 having 150 nm. As a comparative example, the conventionalstructure shown in FIG. 1 (a disk (O)) having no barrier layer issimilarly produced, and it is compared to the disks (1) and (3). Thedisk (0) is provided with the dielectric protective layers 2 and 4comprising the mixture of ZnS and SiO₂, and each layer film thickness is91 nm and 17.7 nm, respectively. Furthermore, the recording layer 3comprising a Ge2Sb2.8Te5 alloy has the film thickness of 20 nm. Thereflecting layer 5 comprising AlCr has the film thickness of 150 nm.

The repeating characteristic of the disks (1), (3), (0) is shown inTable 4. In Table 4, the repeating record characteristic is examined bythe following method. That is, as described above, the EFM signal systemis used. When the shortest mark length becomes 0.61 μm, the marks 3T to11T are recorded. ⊚. The value resulted from dividing the jitter valuebetween each front end and the jitter value between each rear end by thewindow width T (henceforth, referred to as the jitter value) isexamined. As a result, the case that after 150,000-time repeatingrecord, both of the jitter value between the front ends and the jittervalue between the rear ends do not exceed 13% is represented by ⊚. Thecase that after 150,000-time repeating, although at least either thejitter value between the front ends or the jitter value between the rearends exceeds 13%, after 100,000-time repeating, both of them do notexceed 13% is represented by 0. The case that after 100,000-timerepeating, at least either the jitter value between the front ends orthe jitter value between the rear ends exceeds 13% is represented by X.Thereby, in the disk provided with the barrier layer 8 having thestructure according to the present invention, compared to the prior art,the repeating characteristic is enhanced.

EXAMPLE 2

All the protective layers at the substrate side of the disk (1) in Table4 in the example 1 are changed to the Ge—N layer or the Ge—N—O layer,thereby a disk (5) is formed (accordingly, the Ge—N protective layer orthe Ge—N—O protective layer whose thickness is 91 nm is formed at thesubstrate side of the recording layer). Furthermore, all the protectivelayers at the reflecting layer side of the disk (3) in Table 4 arechanged to the Ge—N layer or the Ge—N—O layer, thereby a disk (6) isformed (accordingly, the Ge—N protective layer or the Ge—N—O protectivelayer whose thickness is 25.2 nm is formed at the reflecting layer sideof the recording layer). The repeating characteristic of disks (5) and(6) is examined by the same method as the example 1. Both of them cansimilarly obtain the result ⊚. That is, the Ge—N layer or the Ge—N—Olayer can be formed in such a manner that the Ge—N layer or the Ge—N—Olayer can obtain a thickness necessary for the protective layer.Furthermore, even in this case, the excellent repeating performance canbe obtained.

EXAMPLE 3

Next, the recording layer 3 comprises a phase change material whose maincomponent is a Ge2Sb2.3Te5 alloy, when the barrier layer 8 is formed, Sbis used as the target, and the mixture of Ar and nitrogen is used as thesputter gas. On the above condition, the films comprising the structureshown in FIGS. 3A and 3B are formed (a disk (2), a disk (4)). In thiscase, the film thickness of each layer is same as the thickness in theabove case that Ge is used as the target. The spatter gas pressure ofthe barrier layer 8 is 20 mTorr, and the partial pressure ratio of Ar tonitrogen in the sputter gas is 3 to 1. In this case, the result of therepeating characteristic is shown in disk numbers (2) and (4) in Table4.

According to Table 4, compared to the case that Ge is used as the targetso that the film is formed, although the number of repeatable times isinferior, better repeating characteristic can be obtained than thecomparative example.

TABLE 4 Result 3 of comparing the characteristics of the optical diskapplying the barrier layer according to the present invention to thoseof the prior art Target of the Repeating Disk Number Layer StructureBarrier Layer Characteristic (0) FIG. 1   No Target X (1) FIG. 3A Ge ⊚(2) FIG. 3A Sb ◯ (3) FIG. 3B Ge ⊚ (4) FIG. 3B Sb ◯

EXAMPLE 4

Next, when the layer structure is constructed as shown in FIG. 3A, andGe is used as the target for forming the barrier layer 8, the range ofthe film formation condition which can obtain a better characteristic isexamined.

According to the embodiment, the total sputter gas pressure isconstantly set to 20 mTorr, and the partial pressure ratio of Ar andnitrogen in the sputter gas has three kinds of ratio, that is, 2:1, 1:1and 1:2. The sputter power of Ge is RF100 W, 300 W, 500 W, 700 W, 710 W,750 W, 1 kW, 1.5 kW and 2 kW. That is, since the target is the discwhose diameter is 10 cm, when the sputter power is converted into thepower density, the respective sputter powers are changed to 1.27 W/cm²3.82 W/cm², 6.37 W/cm², 8.91 W/cm², 9.04 W/cm², 9.55 kW/cm², 12.7 kW/cm²19.1 kW/cm² and 25.5 W/cm², respectively. Thereby, the film is formed,and the characteristic of the disks is examined. When the partial ratioof Ar and nitrogen is changed to 2:1, 1:1 and 1:2, respectively, theflow rate of nitrogen is constantly set to 50 sccm, and the flow rate ofAr is changed to 100 sccm, 50 sccm and 25 sccm corresponding to the flowrate of nitrogen 50 sccm. The main valve of the vacuum pump isthrottled, thereby the sputter gas total pressure is set to 20 mTorr.

The layer structure is constructed similarly to the disks (1) and (2).The film thickness of each layer is as follows. The dielectric layer 2is 86 nm, the barrier layer 8 is 5 nm, the recording layer 3 is 20 nm,the dielectric layer 4 is 17.7 nm and the reflecting layer 5 is 150 nm.The repeating characteristic is examined by the method shown in theexample 1. The result is shown in Table 5. Furthermore, the adhesivenessis adopted as the estimate item of the weather-proof The accelerationtest is carried out at 90° C. at 80%, a sampling is carried out in 100hours, 150 hours and 200 hours, and the sample is observed with anoptical microscope in order to find whether the peeling exists or not.The result is shown in Table 6A. In this case, the generated peeling issubstantially ranging from 1 μm to 10 μm. ⊚ denotes the case that thesampling after 200 hours is not peeled at all. ∘ denotes the case thatalthough the sampling after 100 hours and 150 hours is not peeled, thesampling after 200 hours is peeled, even if slightly. A denotes the casethat although the sampling after 100 hours is not peeled, the samplingafter 150 hours is peeled, even if slightly. X denotes the case that thesampling after 100 hours is peeled, even if slightly.

TABLE 5 Relationship between a film formation condition of a barrierlayer applied to a substrate side of a recording layer and a cycleperformance Sputter Power (Ar partial pressure):(Nitrogen partialpressure) (W) 2:1 1:1 1:2 100 X X X 300 ◯ ◯ X 500 ◯ ◯ X 700 ◯ ◯ X 710 ◯◯ ◯ 750 ◯ ◯ ◯ 1000  ◯ ◯ ◯ 1500  ◯ ◯ ◯ 2000  ◯ ◯ ◯

TABLE 6A Relationship between a condition of forming a film of a barrierlayer applied to a substrate side of a recording layer and aweatherproof Sputter Power (Ar partial pressure):(Nitrogen partialpressure) (W) 2:1 1:1 1:2 100 ◯ ◯ X 300 ◯ ◯ X 500 ◯ ◯ X 700 ⊚ ◯ X 710 ⊚⊚ Δ 750 ⊚ ⊚ ◯ 1000  ⊚ ⊚ ◯ 1500  ⊚ ⊚ ⊚ 2000  ⊚ ⊚ ⊚

Thereby, in view of the repeating characteristic, when the sputter poweris more than RF300 W, better characteristic can be obtained. In view ofthe adhesiveness, when the sputter power is more than RF100 W, bettergood characteristic can be obtained. In either cases, the higher thesputter power becomes, the better the characteristic can be obtained.This reason is that the higher the sputter power becomes, the denserfilm can be formed.

Relating to the nitrogen partial pressure, in case of (Ar partialpressure): (nitrogen partial pressure)=1:2, better characteristic can beobtained only within the sputter power range more than 710 W. When thenitrogen partial pressure is higher than an appropriate condition, sincea surplus nitrogen not combined to Ge exists in the barrier layer, it isassumed that the peeling is generated due to the surplus nitrogen. Onthe same condition of the nitrogen partial pressure, when the sputterpower is increased, there is reduced a possibility that the Ge atomsputtered on the target surface is combined to the nitrogen until thesputtered Ge atom is attached to the substrate surface. Thereby, since amixture amount of the surplus nitrogen is reduced, it is expected thatthe region where better characteristic can be obtained exists.

As an analyzing result of the average composition ratio of the barrierlayer 8 which can obtain better characteristic, in any case, the averagecomposition ratio of Ge, O and N is within the range surrounded by fourcomposition points shown the three-element composition diagram in FIG.5, E1(Ge_(50.0)N_(50.0)), G1(Ge_(35.0)N_(65.0))G4(Ge_(31.1)N_(13.8)O_(55.1)), E4(Ge_(42.3)N_(11.5)O_(46.2)). Ingeneral, when Ge or Ge—N is used as the target and the mixed gas of therare gas and nitrogen is provided so that the film is formed, there is atendency that if the sputter power is relatively small, the Ge—N—O filmcontaining a lot of oxygen is formed, and if the sputter power isrelatively large, the Ge—N film whose oxygen-content is only an impuritylevel is formed.

As described above, preferably, the sputter power has the power densitymore than 1.27 W/cm². When the power density is more than 3.82 W/cm²,better adhesiveness and recorded repeating characteristic can beobtained. In this case, a film formation rate is 18 nm/minute, when Arpartial pressure: nitrogen partial pressure=1:1. Preferably, the filmformation rate is 18 nm/minute or more.

EXAMPLE 5

Next, the difference of the disk characteristic is examined according tothe difference of the partial pressure ratio of the sputter gas pressureand the nitrogen partial pressure in the sputter gas. Thus, the layerstructure comprises the same structure in FIGS. 3A and 3E. Ge is used asthe target, and the sputter power is constantly set to RF700 W. When thetotal pressure of the sputter gas, Ar partial pressure and the nitrogenpartial pressure are changed, the characteristic is examined. A FIG.3A-type disk comprises a ZnS—SiO₂ protective layer whose film thicknessis 86 nm, a Ge—N or Ge—N—O barrier layer whose film thickness is 5 nm, aGe—Sb—Te recording layer whose film thickness is 20 nm, a ZnS—SiO₂protective layer whose film thickness is 17.7 nm and an AlCr reflectinglayer whose film thickness is 150 nm. A FIG. 3E-type disk comprises aZnS—SiO₂ protective layer whose film thickness is 91 nm, a Ge—Sb—Terecording layer whose film thickness is 20 nm, a Ge—N or Ge—N—O barrierlayer whose film thickness is 17.7 nm, and an AlCr reflecting layerwhose film thickness is 150 nm.

The repeating characteristic is estimated by the same method as theexample 1 to 3. The weather-proof is estimated by the same method as theexample 4. Table 6B shows the film formation condition and the estimateresult. In Table 6B the disk (O) denotes the conventional disk in theexample 1. Furthermore, marks are represented two by two, where the leftmark and the right mark correspond to the result of the FIG. 3A-typedisk and the result of the FIG. 3E-type disk, respectively.

TABLE 6B Relationship between a sputter condition of a barrier layerapplied to a substrate side of a recording layer and a disk performanceTotal Partial Repeating pressure pressure Weather-proof characteristicDisk No. (mTorr) ratio 2A 2E 2A 2E  (0) — — ⊚ X  (5) 1.0 1:2 X X X X (6) 3.0 1:2 X X X X  (7) 10.0 1:2 X X X X  (8) 20.0 1:2 X X X X  (9)30.0 1:2 X X X X (10) 1.0 2:3 Δ X X X (11) 3.0 2:3 Δ X ◯ ◯ (12) 10.0 2:3Δ X ◯ ◯ (13) 20.0 2:3 Δ X ◯ ◯ (14) 30.0 2:3 Δ X ◯ ◯ (15) 1.0 1:1 ◯ Δ X X(16) 3.0 1:1 ◯ Δ ◯ ◯ (17) 10.0 1:1 ◯ Δ ◯ ◯ (18) 20.0 1:1 ◯ Δ ◯ ◯ (19)30.0 1:1 ◯ Δ ◯ ◯ (20) 1.0 3:2 ◯ Δ ◯ ◯ (21) 3.0 3:2 ◯ Δ ◯ ◯ (22) 10.0 3:2◯ Δ ◯ ◯ (23) 20.0 3:2 ◯ Δ ◯ ◯ (24) 30.0 3:2 ◯ Δ ◯ ◯ (25) 1.0 2:1 ⊚ ◯ X X(26) 3.0 2:1 ⊚ ◯ ◯ ◯ (27) 10.0 2:1 ⊚ ◯ ◯ ◯ (28) 20.0 2:1 ⊚ ◯ ◯ ◯ (29)30.0 2:1 ⊚ ◯ ◯ ◯ (30) 20.0 80:20 ⊚ ⊚ ◯ ◯ (31) 20.0 85:15 ⊚ ⊚ ◯ ◯ (32)20.0 88:12 ⊚ ⊚ ◯ ◯ (33) 20.0 90:10 ⊚ ⊚ X ◯ (34) 20.0 95:5  ⊚ ⊚ X ◯ (35)20.0 100:0  ⊚ ⊚ X X (36) 10.0 75:25 ⊚ ⊚ ◯ ◯ (37) 10.0 80:20 ⊚ ⊚ X ◯ (38)10.0 85:15 ⊚ ⊚ X ◯ (39) 10.0 90:10 ⊚ ⊚ X X (40) 10.0 100:0  ⊚ ⊚ X X

FIGS. 10 and 11, and FIGS. 12 and 13 show respective cases of therepeating characteristic and the weather-proof. Here, the nitrogenpartial pressure is represented by an abscissa axis, and Ar partialpressure is represented by an ordinate axis.

In the first place, in case of the 3A-type disk as shown in FIG. 10, thefilm formation condition which can obtain better repeatingcharacteristic is the case that the total pressure of the sputter gasexceeds 1 mTorr. Furthermore, when the total pressure is 10 mTorr, thenitrogen gas partial pressure in the sputter gas is ranging from 25% to60%. Furthermore, when the total pressure is 20 mTorr, the nitrogen gaspartial pressure in the sputter gas is ranging from 12% to 60%.

Furthermore, as shown in FIG. 12, the film formation condition which canobtain better weather-proof (adhesiveness) is the case that the totalpressure of the sputter gas is more than 1 mTorr, similarly to the caseof the repeating characteristic. In both cases of the total pressure 10mTorr and the total pressure 20 mTorr, similarly, the nitrogen gaspartial pressure in the sputter gas is within the range of 60% or less,preferably 50% or less.

Next, in case of the 3E-type disk, as shown in FIG. 11, the filmformation of the barrier layer condition which can obtain betterrepeating characteristic is the case that the total pressure of thesputter gas exceeds 1 mTorr. Furthermore, when the total pressure is 10mTorr, the nitrogen gas partial pressure in the sputter gas is rangingfrom 15% to 60%. Furthermore, when the total pressure is 20 mTorr, thenitrogen gas partial pressure in the sputter gas is ranging from 5% to60%. Furthermore, as shown in FIG. 13, the film formation conditionwhich can obtain better weather-proof (adhesiveness) is the case thatthe total pressure of the sputter gas is 1 mTorr or more, similarly tothe case of the repeating characteristic. In both cases of the totalpressure 10 mTorr and the total pressure 20 mTorr, similarly, thenitrogen gas partial pressure in the sputter gas is within the range of40% or less, preferably 33% or less.

According to this analysis, the composition range of the Ge—N or Ge—N—Olayer which can obtain better characteristic is examined. When thismaterial layer is disposed at the substrate side of the recording layer,as shown in the triangular composition diagram shown in FIG. 5, theaverage composition ratio is within the region surrounded by fourpoints, D1(Ge_(60.0)N_(40.0)), D4(Ge_(48.8)N_(10.2)O_(41.0)),G1(Ge_(35.0)N_(65.0)), G4(Ge_(31.1)N_(13.8)O_(55.1)).

Furthermore, when the material layer is disposed at the side opposite tothe substrate of the recording layer, the average composition ratio iswithin the range surrounded by four composition points,B1(Ge_(90.0)N_(10.0)), B4(Ge_(83.4)N_(3.3)O_(13.3))F1(Ge_(42.9)N_(57.1)), F4(Ge_(35.5)N_(12.9)O_(51.6)), more preferably,the composition range surrounded by four composition points,C1(Ge_(65.0)N_(35.0)C4(Ge_(53.9)N_(9.2)O_(36.9)), F1(Ge_(42.9)N_(57.1)),F4(Ge_(35.5)N_(12.9)O_(51.6)).

Regarding the repeating characteristic, when the nitrogen partialpressure in the sputter gas is low, since a lot of surplus Ge notconnected to the nitrogen exists in the barrier layer. Accordingly, thecomposition of the recording layer is changed, accompanied by therewrite of the signal. Thereby, better characteristic cannot beobtained. Since a temperature rise at the reflecting layer side of therecording layer is lower than that at the substrate side, a degree ofthe atom diffusion is relatively small, thereby the condition that theN₂ partial pressure is low can be used. On the contrary, when thenitrogen partial pressure in the sputter gas is too high, a lot ofsurplus nitrogen exists in the film. In this case, better repeatingcharacteristic cannot be obtained.

Regarding the adhesiveness, when the nitrogen partial pressure in thesputter gas is high and a lot of surplus nitrogen exists in the film,the peeling is generated after the acceleration test. When the nitrogenpartial pressure is low and the surplus Ge not combined to the nitrogenexists, the peeling is not generated. It is expected that the more Genot combined to the nitrogen and oxygen exists, the higher an affinityfor the recording layer component becomes.

As described above, in order to obtain the disk having better repeatingcharacteristic of the record and the adhesiveness, the sputter gascondition (gas pressure, component ratio) is clear. When the sputter gastotal pressure exceeds 50 mTorr, the film formation rate becomes small.Accordingly, it is not practical.

The film formation condition is the case that when the Ge—N or Ge—N—Olayer is formed, the power density to be introduced into the target is8.91 W/cm². When the power to be introduced into the target is more than8.91 W/cm², a time until the Ge atom sputtered on the target surface isattached to the substrate surface becomes shorter than the above case,thereby nitriding and nitriding-oxidation are hardly generated. In thiscase, according to the rate, the nitrogen partial pressure in thesputter gas is appropriately increased, thereby the similar effect tothe case that the power density is 8.91 W/cm² can be obtained. On thecontrary, when the introducing power is less than 8.91 W/cm², since thenitriding and nitriding-oxidation are excessively generated, accordingto the rate, the nitrogen partial pressure can be only adjusted in sucha manner that the nitrogen partial pressure of the sputter gas isappropriately reduced.

When the nitrogen partial pressure ratio in the sputter gas is more thanabout 90%, the sputtering is more or less unstable and it is notpreferable. The value of the sputter power and the film formation rateis set to an optional value within the range in which the nitride ornitride-oxide can be formed. As described above, preferably, the sputterpower density exceeds 1.27 W/cm², and the film formation rate is 18nm/minute or more.

EXAMPLE 6

Next, when the film formation condition is changed, the change of theoptical constant of the barrier layer is examined. In the first place,the sputter power of Ge is set to 700 W, and the sputter total pressureis constantly set to 20 mTorr. When the nitrogen partial pressure ratioin the sputter gas is changed, that is, the change of the complexrefractive index of the film on a line a in FIGS. 10 and 11 is examined.The result is shown in FIG. 14. Furthermore, the sputter power is 700 W,and the sputter total pressure is constantly set to 10 mTorr. When thenitrogen partial pressure ratio in the sputter gas is changed, that is,the change of the complex refractive index of the film on a line a′ inFIGS. 10 and 11 is examined. The result is shown in FIG. 15. Next, thepartial pressure ratio of Ar and the nitrogen in the sputter gas isconstantly set to 1:1, and the gas total pressure is changed. In thiscase, FIG. 16 shows the change of the optical constant of the film on aline b in FIGS. 10 and 11.

These graphs are combined to the above application range of the nitrogenpartial pressure. When the barrier layer is used at the substrate sideof the recording layer, preferably, the complex refractive index valuen+ik of the barrier layer satisfies the range of 1.7≦n≦2.8 and 0≦k≦0.3.Furthermore when the barrier layer is used at the side opposite to thesubstrate of the recording layer, preferably, the complex refractiveindex value n+ik of the barrier layer satisfies the range of 1.7≦n≦3.8and 0≦k≦0.8.

When the film composition is analyzed, if the film is formed by usingthe sputter total pressure 10 mTorr, the oxygen density is ranging aboutfrom 5% to 8%. In case of the sputter total pressure 20 mTorr, theoxygen density is ranging about from 10% to 20%, which is little morethan the case of 10 mTorr.

In view of producing method, even if the film formation condition suchas the sputter power, the sputter gas or the like is changed, the filmis formed in such a manner that the complex refractive index of the Ge—Nfilm or the Ge—O—N film satisfies the above range. Thereby, bettercharacteristic can be obtained.

EXAMPLE 7

Next, except that the structure comprises a barrier layers 8 whose filmthickness are 10 nm, 20 nm, respectively, and a ZnS—SiO₂ protectivelayers 2 of the substrate side whose film thickness are 81 nm, 65.8 nm,respectively, a 2A-type disk having the same layer structure and thefilm thickness as the example 4 is produced. The film formationcondition of the barrier layer 8 is as follows: the sputter power isRF700 W, that is, the power density 8.91 W/cm², the sputter gas totalpressure is 20 mTorr, Ar partial pressure : the nitrogen partialpressure=2:1, and the gas flow rate is similar to the above case.

As a result of examining the repeating characteristic and theweather-proof of the disk, similarly to the above case, a very goodcharacteristic can be obtained.

EXAMPLE 8

Next, the effect when the barrier layer is applied is shown by comparingthe disks having different layer structure to one another. Table 7 showsthe structure of the experimentally made disks and the estimate resultof the cycle performance thereof. In Table 7, DL denotes the protectivelayer containing ZnS—SiO₂, AL denotes the recording layer containingGe2Sb2.2Te5, BL denotes the barrier layer containing Ge50N₄₅₀₅, and RLdenotes the reflecting layer containing AlCr. More specifically, whenthe material is changed or the material is specified, the descriptionsuch as DL(Ge—N—O) is included in parentheses.

The estimate method is the same as the case of Table 2. That is, thejitter value and the amplitude value are estimated. After 100,000-timerepeating record, the jitter value (measured by such a method that thejitter between each mark front end and the jitter between each mark rearend are independently measured) is estimated. Such a case that both ofthe jitter between the mark front ends and the jitter between the markrear ends are less than a reference value and the jitter value isscarcely changed is represented by ⊚. Such a case that although thejitter value is changed, the jitter value itself remains less than thereference value is represented by ∘. Such a case that after 100,000-timerepeating, the jitter slightly exceeds the reference value isrepresented by Δ. Such a case that after 10,000-time repeating, thejitter value already exceeds the reference value is represented by X.The estimate power is set to a higher value by about 10% than the lowestlimit jitter value, where the lowest limit jitter value denotes thevalue when an initial jitter value satisfies the value less than 12.8%.Furthermore, after 100,000-time repeating, the amplitude value isobserved. Such a case that less change is found is represented by ⊚.Such a case that about 10% or less change is found is represented by ∘.Such a case that about 20% change is found is represented by Δ. Such acase that the jitter value is reduced to more than 20% is represented byX. Table 7 shows the followings:

1) in case of no reflecting layer (a disk 41), the amplitude value isseverely reduced, and the jitter value rise is large. However, thebarrier layer is provided, thereby it is possible to obtain aconsiderable effect of the jitter performance and the amplitudeperformance (disks 42 and 43), 2) even if the reflecting layer isprovided, when the reflecting layer id thin, or if the layer between thereflecting layer and the recording layer is thick (a disk 44: ingeneral, a so-called annealing structure), the same effect as the casethat the reflecting layer is thick or the layer between the reflectinglayer and the recording layer is thin (a disk 47: in general, aso-called quenching structure) cannot be obtained,

3) if the barrier layer is applied to the annealing structure, aconsiderable effect can be obtained (disks 45 and 46),

4) in the quenching structure, the barrier layer is only disposed at oneside of the recording layer, thereby the considerable effect can beobtained.

That is, in the structure having no reflecting layer or in the structurein which the protective layer having a thickness (for example, 80 nm ormore) is formed between the recording layer and the reflecting layer,the barrier layer is considerably effective relative to the jitter valuereduction and to the suppression of the amplitude reduction due to therepeating record. When many repeating times is necessary, the barrierlayer is essential. Recently, in many cases, the above annealingstructure can be applied to the optical disk overwriting at a high speed(for example, Noboru Yamada et al. “Thermally balanced structure ofphase-change optical disk for high speed and high density recording.”Trans. Mat. Res. Soc. Jpn., Vol. 15B, 1035, (1993)). Accordingly, acombination of the annealing structure and barrier layer generates alarge effect.

On the other hand, the structure having a thin protective layer (forexample, 60 nm or less) formed between the recording layer and thereflecting layer is provided with the barrier layer as the protectivelayer. Thereby, more specifically, the amplitude performance can beenhanced. Accordingly, much more repeating times can be achieved.

TABLE 7 Effect comparison of the barrier layer relative to various layerstructure Repeating Disk performance number Disk layer structure JitterAmplitude 41 DL AL DL X X 90 nm 22 nm 82 nm 42 DL BL AL DL ◯ ◯ 80 nm 10nm 22 nm 82 nm 43 DL BL AL DL DL ⊚ ⊚ 80 nm 10 nm 22 nm 10 nm 72 nm 44 DLAL DL RL(Au) Δ X 90 nm 22 nm 80 nm 10 nm 45 DL BL AL DL RL(Au) ◯ ◯ 80 nm10 nm 22 nm 90 nm 10 nm 46 DL BL AL DL(GeNO) RL(Au) ⊚ ⊚ 80 nm 10 nm 22nm 90 nm 10 nm 47 DL AL DL RL ◯ Δ 90 nm 22 nm 60 nm 150 nm  48 DL BL ALDL RL ⊚ ⊚ 90 nm 10 nm 22 nm 60 nm 150 nm  49 DL AL DL(GeNO) RL ⊚ ⊚ 90 nm22 nm 60 nm 150 nm  50 DL BL AL DL(GeNO) RL ⊚ ⊚ 90 nm 10 nm 22 nm 60 nm150 nm 

EXAMPLE 9

Whether or not the material layer except for the Ge—N, Ge—N—O layer canbe used as the barrier layer is examined. As a material candidate, Si—N,Si—N—O, Sic, Sb—N—O, Zr—N—O, Ti—N, Al—N and Al—N—O are selected. In anycase, the sputter condition is selected. Two kinds of compositions, thatis, (A) a stoichiometric composition and (B) the composition containingabout 5% more Si, Al, Ti, or the like than the stoichiometriccomposition are tested. The medium structure is a FIG. 3G-typestructure. The barrier layer has the thickness of 10 nm. The mediumstructure comprises a ZnSe—SiO₂ protective layer whose thickness is 80nm, the barrier layer, a Ge2Sb2.5Te5 recording layer whose thickness is20 nm, a barrier material layer whose thickness is 20 nm, and an Aureflecting layer whose thickness is 50 nm deposited on a polycarbidesubstrate whose thickness is 1.2 mm by the sputtering method. Afterovercoating, a hot melt adhesive is used so that a defense plate islaminated. Next an initial crystallization is carried out by the lasermethod. Furthermore for a comparison, the structure in which the barrierlayer is not used is also prepared. These disks are rotated at a linearrate of 3.5 m/s, and an EFM signal (random signal) having the 3T markwhose length is 0.6 μm is repeatedly overwritten, and the cycleperformance is estimated. Furthermore, these disks are left to standunder the acceleration condition of 90° C. and 80% RH for 100 hours, andthe state of the disks is estimated.

The result is shown in Table 8. In Table 8, regarding the cycleperformance, ∘ means that after 100,000-repeating, the effect isobtained. That is, there is such an advancement that the jitter valuerise and the amplitude value reduction are clearly less than thereference value. A means that a little effect is obtained. X means thatno effect is obtained. Furthermore, regarding the weather-proof, ∘ meansthat no change is detected. X means that such a change as the peeling,etc. is detected. Δ means that a little change such as the peeling, etc.is detected. Thus, regarding the cycle performance, there is a tendencythat both of groups (A) and (B) are improved. Regarding theweather-proof, the group (B) is sprier to the group (A), that is, thereis more possibility that the composition containing little less N, O orthe like than the stoichiometric composition can be applied to thebarrier layer.

TABLE 8 Comparison of barrier materials A B Material Weather- Weather-composition Cycle proof Cycle proof 51 Si—N Δ X Δ Δ 52 Si—N—O Δ X ◯ ◯ 53SiC Δ X ◯ Δ 54 Sb—N Δ X Δ ◯ 55 Sb—N—O Δ X Δ ◯ 56 Zr—N Δ X ◯ ◯ 57 Zr—N—OΔ X ◯ ◯ 58 Ti—N Δ X ◯ Δ 59 Al—N Δ X ◯ Δ 60 Al—N—O Δ X ◯ ◯

As described above, according to the present invention, it is possibleto provide the optical information recording medium in which the changeof the recording characteristic and the reproducing characteristic dueto repeating the record and reproduction is lower and further theweatherproof is excellent, the producing method thereof and a method ofrecording and reproducing the information.

EXAMPLE 10

In the Examples, the weather resistance and the characteristics inrepetitive recording were evaluated in the following manner. For theevaluation of the weather resistance, an accelerated test was performedat 90° C. and 80% humidity for 200 hours, and it was observed with anoptical microscope at every 100 hours whether or not the peeling of thefilm occurred. As a result, examined samples were classified into “A”,“B” and “C”. In a sample denoted by “A”, no peeling was observed for 200hours. In a sample denoted by “B”, no peeling was observed for the first100 hours but peeling occurred after 200 hours. In a sample denoted by“C”, peeling occurred after 100 hours.

For the evaluation of the characteristics in repetitive recording,random marks having lengths from 3T to 11T when the minimum mark lengthis 0.61 μm in EFM signal system were recorded. In a sample denoted by“A”, neither the ratio of a jitter value between front ends of the marksto a window width T nor the ratio of a jitter value between rear ends toa window width T exceeded 13% after 200,000 times repetitive recording.In a sample denoted by “B”, neither of the ratios for the front ends orthe rear ends exceeded 13% after 100,000 times repetitive recording, butat least one of the ratios for the front ends and the rear ends exceeded13% after 200,000 times repetitive recording. In a sample denoted by“C”, at least one of the ratios for the front ends and the rear endsexceeded 13% after 100,000 times repetitive recording.

The optical information recording medium having the same structure asshown in FIG. 1 was produced by sputtering as described above. Adisk-shaped polycarbonate resin having a thickness of 0.6 mm and adiameter of 120 mm was used for a substrate 61. A material comprisingZnS and 20 mol % of SiO₂ was used for a protective layer 62. Aphase-changeable material comprising Ge—Sb—Te alloy was used for arecording layer 63, and an Al alloy was used for a reflection layer 65.The composition of the recording layer 63 wasGe_(22.0)Sb_(25.0)Te_(53.0) in this example, but other compositions canbe used.

A medium comprising a diffusion preventing layer 67 formed of GeN and adiffusion preventing layer 68 formed of GeNiN was referred to as sample101. A medium comprising a diffusion preventing layer 67 formed of GeNand a diffusion preventing layer 68 formed of GeCrN was referred to assample 102. A medium comprising a diffusion preventing layer 67 formedof GeN and a diffusion preventing layer 68 formed of GeCoN was referredto as sample 103. A medium comprising a diffusion preventing layer 67formed of GeN and a diffusion preventing layer 68 formed of GeMoN wasreferred to as sample 104. A medium comprising a diffusion preventinglayer 67 formed of GeN and a diffusion preventing layer 68 formed ofGeMnN was referred to as sample 105. A medium comprising a diffusionpreventing layer 67 formed of GeN and a diffusion preventing layer 68formed of GeLaN was referred to as sample 106. A medium comprising adiffusion preventing layer 67 formed of GeN and a diffusion preventinglayer 68 formed of GeTiN was referred to as sample 107. A mediumcomprising a diffusion preventing layer 67 formed of GeN and a diffusionpreventing layer 68 formed of GeZrN was referred to as sample 108. Amedium comprising a diffusion preventing layer 67 formed of GeN and adiffusion preventing layer 68 formed of GeNbN was referred to as sample109. For comparison, sample 100 comprising diffusion preventing layers67 and 68 both formed of GeN was produced.

When forming a GeMN layer (M=Ni, Cr, Co, Mo, Mn, La, Ti, Zr or Nb) and aGeN layer, GeM and Ge, respectively, were used as target materials, andthe content of M contained in the GeMN layer was 25 atom % of the totalcontent of Ge and M. This ratio was analyzed by ICP (ICP EmissionSpectrometry).

Furthermore, the thicknesses of the diffusion preventing layers 67 and68 of samples 100 to 109 were 10 nm and 20 nm, respectively, which werecommon between samples 100 to 109. Similarly, there was no differencebetween samples 100 to 109 for the thickness of the protective layer 2of 120 nm, the thickness of the recording layer 3 of 20 nm, and thethickness of the reflection layer 5 of 150 nm.

In order to form the protective layer 62 and the recording layer 63, amixed gas comprising Ar and 2.5 vol % of nitrogen was supplied at aconstant flow rate and a total pressure of 1.0 mTorr and 0.5 mTorr,respectively, and DC powers of 1.27 W/cm² and RF 5.10 W/cm²,respectively, were supplied to cathodes. The nitrogen gas was mixed withthe sputtering gas in order to suppress the movement of the substancesin the medium after repetitive recording. The advantageous effect of thepresent invention can be obtained in the case where nitrogen is notsupplied from the sputtering gas or oxygen is mixed with the sputteringgas. In order to form the reflection layer 65, Ar gas was supplied at atotal pressure of 3.0 mTorr, and a DC power of 4.45 W/cm² was supplied.Other rare gases than Ar such as Kr can be contained in the sputteringgas, as long as it allows sputtering.

When forming the diffusion preventing layers 67 and 68, there was nodifference between samples 100 to 109 as to the sputtering gas, whichwas a mixed gas comprising Ar and nitrogen, a sputtering gas pressure of10 mTorr, and a sputtering power density of 6.37 W/cm². When forming thediffusion preventing layer 67, the partial pressure of nitrogen in thesputtering gas was constantly 40% (40 vol % nitrogen). When forming thediffusion preventing layer 68, the partial pressure of nitrogen in thesputtering gas was changed to 10%, 20%, 30% and 40%. In this case, thecontents of nitrogen contained in the diffusion preventing layers 67 and68 were 22 atom %, 37 atom %, 50 atom %, and 56 atom %, respectively.Furthermore, the contents of oxygen contained in the diffusionpreventing layers 67 and 68 were 4 atom %, 5 atom %, 6 atom %, and 7atom %, respectively. The oxygen was contained because impurity oxygenpresent in the chamber was absorbed in the layers. The ratios ofnitrogen and oxygen were analyzed by RBS (Rutherford BackscatteringSpectroscopy).

The results of the evaluation of the characteristics of the produceddisk-shaped media are shown in Table 9.

TABLE 9 Diffusion Partial Pressure of Nitrogen in Film- preventingForming Gas layer 10% 20% 30% 40% Medium No. 67 68 a* b* a* b* a* b* a*b* Sample 100 GeN GeN A B A A B A C A Sample 101 GeN GeNiN A B A A A A AA Sample 102 GeN GeCrN A B A A A A A A Sample 103 GeN GeCoN A B A A A AB A Sample 104 GeN GeMoN A B A A A A B A Sample 105 GeN GeMnN A B A A AA B A Sample 106 GeN GeLaN A B A A A A B A Sample 107 GeN GeTiN A B A AA A B A Sample 108 GeN GeZrN A B A A A A B A Sample 109 GeN GeNbN A B AA A A B A a*: Weather resistance b*: Repetition characteristics

Furthermore, samples 110 to 118 were produced under the same conditionsas samples 101 to 109, except that the diffusion preventing layer 68 isformed of GeN, the diffusion preventing layer 67 is formed of GeMN (Mrepresents the elements as described above), when forming the diffusionpreventing layer 68, the partial pressure of nitrogen in the sputteringgas was constantly 30%, and when forming the diffusion preventing layer67, the partial pressure of nitrogen in the sputtering gas was changedto 40%, 50% and 60%. Sample 100′ is a medium in which the diffusionpreventing layers 67 and 68 were both formed of GeN. Table 10 shows theresults of the evaluation of these media.

TABLE 10 Diffusion Partial Pressure of Nitrogen preventing inFilm-Forming Gas layer 40% 50% 60% Medium No. 67 68 a* b* a* b* a* b*Sample 100′ GeN GeN B A B A C A Sample 110 GeNiN GeN A A A A A A Sample111 GeCrN GeN A A A A A A Sample 112 GeCoN GeN A A A A A A Sample 113GeMoN GeN A A A A A A Sample 114 GeMnN GeN A A A A A A Sample 115 GeLaNGeN A A A A A A Sample 116 GeTiN GeN A A A A B A Sample 117 GeZrN GeN AA A A B A Sample 118 GeNbN GeN A A A A B A a*: Weather resistance b*:Repetition characteristics

As seen from the results shown in Tables 9 and 10, when GeMN is used forthe diffusion preventing layer, weather resistance is improved withoutimpairing the repetition characteristics in recording, compared with thediffusion layer formed of GeN.

Next, disks including the diffusion preventing layers 67 and 68 formedof GeN and GeCrN, respectively, and having different ratios of thecontent of Cr to the total content of Ge and Cr in the GeCrN layer of5%, 10%, 20%, 30%, 40%, 50%, and 60% were produced. These media werereferred to as samples 119, 120, 121, 122, 123, 124 and 125. Thestructures of the layers of the disks were the same as that of the diskof sample 102. When forming the diffusion preventing layer 67, thepartial pressure of nitrogen in the sputtering gas was constantly 40%.When forming the diffusion preventing layer 68, the partial pressure ofnitrogen in the sputtering gas was changed to 20%, 30% and 40%. Table 11shows the results of the evaluation of the disks.

TABLE 11 Partial Pressure of Nitrogen in Film-Forming Gas Cr/ 20% 30%40% Medium No. (Ge + Cr) a* b* a* b* a* b* Sample 100  0 A A B A C ASample 119  5 A A B A B A Sample 120 10 A A A A A A Sample 121 20 A A AA A A Sample 122 30 A A A A A A Sample 123 40 A A A A A A Sample 124 50A B A A A A Sample 125 60 A C A B A B a*: Weather resistance b*:Repetition characteristics

Table 11 reveals that when the content of Cr is 10% or more, the effectof the addition of Cr is particularly desirable. However, when thecontent of Cr is 60% or more, the repetition characteristicsdeteriorate. This is believed to be because Cr atoms, which aredifficult to be bonded to nitrogen compared with Ge atoms, wereexcessively present in the film, so that the Cr atoms flooded into therecording layer so as to deteriorate the characteristics in repetitiverecording. Therefore, the content of Cr in the GeCrN film is preferably50% or less, more preferably 40% or less of the total content of Ge andCr.

Next, disks were produced in the same manner except that Mo or Ti wasused in place of Cr. Tables 12 and 13 show the results of the evaluationof the thus produced disks.

TABLE 12 Partial Pressure of Nitrogen in Film-Forming Gas Mo/ 20% 30%40% Medium No. (Ge + Mo) a* b* a* b* a* b* Sample 100  0 A A B A C ASample 126  5 A A B A B A Sample 127 10 A A A A B A Sample 128 20 A A AA B A Sample 129 30 A A A A B A Sample 130 40 A A A A B A Sample 131 50A A A A B A Sample 132 60 A C A B B B a*: Weather resistance b*:Repetition characteristics

TABLE 13 Partial Pressure of Nitrogen in Film-Forming Gas Ti/ 20% 30%40% Medium No. (Ge + Ti) a* b* a* b* a* b* Sample 100  0 A A B A C ASample 133  5 A A B A B A Sample 134 10 A A A A B A Sample 135 20 A A AA B A Sample 136 30 A A A A B A Sample 137 40 A A A A B A Sample 138 50A B A B B B Sample 139 60 A C A B B B a*: Weather resistance b*:Repetition characteristics

EXAMPLE 11

Optical information recording media were produced in the same manner asin Example 10 except that the diffusion preventing layers were changedas follows.

A medium comprising a diffusion preventing layer 67 formed of GeON and adiffusion preventing layer 68 formed of GeNiON was referred to as sample140. A medium comprising a diffusion preventing layer 67 formed of GeONand a diffusion preventing layer 68 formed of GeCrON was referred to assample 141. A medium comprising a diffusion preventing layer 67 formedof GeON and a diffusion preventing layer 68 formed of GeCoON wasreferred to as sample 142. A medium comprising a diffusion preventinglayer 67 formed of GeON and a diffusion preventing layer 68 formed ofGeMoON was referred to as sample 143. A medium comprising a diffusionpreventing layer 67 formed of GeON and a diffusion preventing layer 68formed of GeMnON was referred to as sample 144. A medium comprising adiffusion preventing layer 67 formed of GeON and a diffusion preventinglayer 68 formed of GeLaON was referred to as sample 145. A mediumcomprising a diffusion preventing layer 67 formed of GeON and adiffusion preventing layer 68 formed of GeTiON was referred to as sample146. A medium comprising a diffusion preventing layer 67 formed of GeONand a diffusion preventing layer 68 formed of GeZrON was referred to assample 147. A medium comprising a diffusion preventing layer 67 formedof GeON and a diffusion preventing layer 68 formed of GeNbON wasreferred to as sample 148. For comparison, sample 100″ comprisingdiffusion preventing layers 67 and 68 both formed of GeON was produced.In this example, the content of M contained in the GeMON layer was 25atom % of the total content of Ge and M.

When forming the diffusion preventing layers 67 and 68, there was nodifference between samples 140 to 148 as to the sputtering gas, whichwas a mixed gas comprising Ar, nitrogen and oxygen, a sputtering gaspressure of 10 mTorr, and a sputtering power density of 6.37 W/cm². Whenforming the diffusion preventing layer 67, the partial pressure ofnitrogen in the sputtering gas was constantly 40% and the partialpressure of oxygen was 3%.

When forming the diffusion preventing layer 68, the partial pressure ofnitrogen in the sputtering gas was changed to 10%, 20%, 30% and 40%, andthe partial pressure of oxygen was constantly 3%. In this case, thecontents of nitrogen contained in the diffusion preventing layer 67 was68 atom % and the contents of oxygen was 20 atom %. Furthermore, thecontents of nitrogen contained in the diffusion preventing layer 68 were24 atom %, 40 atom %, 51 atom % and 58 atom %, respectively. Thecontents of oxygen contained in the diffusion preventing layer 68 were 8atom %, 13 atom %, 17 atom % and 20 atom %, respectively.

The results of the evaluation of the characteristics of the produceddisk-shaped media are shown in Table 14.

TABLE 14 Diffusion Partial Pressure of Nitrogen in Film- preventingForming Gas layer 10% 20% 30% 40% Medium No. 67 68 a* b* a* b* a* b* a*b* Sample 100″ GeON GeON A A B A C A C A Sample 140 GeON GeNiON A A A AA A B A Sample 141 GeON GeCrON A A A A A A B A Sample 142 GeON GeCoON AA A A A A B A Sample 143 GeON GeMoON A A A A A A B A Sample 144 GeONGeMnON A A A A A A B A Sample 145 GeON GeLaON A A A A A A B A Sample 146GeON GeTiON A A A A B A B A Sample 147 GeON GeZrON A A A A B A B ASample 148 GeON GeNbON A A A A B A B A a*: Weather resistance b*:Repetition characteristics

As seen from Table 14, when GeMON is used for the diffusion preventinglayer, the weather resistance is improved without impairing thecharacteristics in repetitive recording compared with the case whereGeON is used. When a layer containing oxygen is used for the diffusionpreventing layer, the repetition characteristics are improved comparedwith the case where the content of oxygen is on an impurity level.However, the weather resistance deteriorates slightly.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limitative, the scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A method of producing a phase change optical information recordingmedium comprising: a) forming a protective layer; b) forming a recordinglayer that generates a reversible phase-change, which can be opticallydetected according to an irradiation of an energy beam; c) forming afirst barrier layer by sputtering using a target containing a barriermaterial in an atmosphere gas containing nitrogen; and d) forming asecond barrier layer by sputtering using a target containing a barriermaterial in an atmosphere gas containing nitrogen; wherein said firstbarrier layer is formed between said protective layer and said recordinglayer, said protective layer comprises sulfur, said recording layer hasa thickness less than or equal to 20 nm and comprises tellurium, saidsecond barrier layer is formed at a side of said recording layeropposite to said first barrier layer; and wherein a nitrogen partialpressure in the atmosphere gas for forming said first barrier layer ishigher than a nitrogen partial pressure in the atmosphere gas forforming said second barrier layer.
 2. A method of producing a phasechange optical information recording medium comprising: a) forming aprotective layer; b) forming a recording layer that generates areversible phase-change, which can be optically detected according to anirradiation of an energy beam; c) forming a first barrier layer bysputtering in a mixed gas containing a rare gas and nitrogen using atarget including at least Ge and X, where X is at least one elementselected from the group consisting of elements belonging to Groups IIIa,IVa, Va, VIa, VIIa, VIII, Ib and IIb and C; and d) forming a secondbarrier layer by sputtering in a mixed gas containing a rare gas andnitrogen using a target including a barrier material; wherein said firstbarrier layer is formed between said protective layer and said recordinglayer, said protective layer comprises sulfur, said recording layer hasa thickness less than or equal to 20 nm and comprises tellurium, saidsecond barrier layer is formed on said recording layer; wherein saidfirst barrier layer comprises either one selected from the groupconsisting of GeXN and GeXON as a main component; and wherein a contentratio of nitrogen in the mixed gas in forming the first barrier layer isdifferent from a content ratio of nitrogen in forming the second barrierlayer.
 3. The method according to claim 2, wherein a content ratio ofnitrogen in the mixed gas in forming the first barrier layer is largerthan a content ratio of nitrogen in the mixed gas forming the secondbarrier layer.
 4. A method of producing a phase change opticalinformation recording medium comprising: a) forming a protective layer;b) forming a recording layer that generates a reversible phase-change,which can be optically detected according to an irradiation of an energybeam; c) forming a first barrier layer by sputtering with a targetincluding at least Ge and X, where X is at least one element selectedfrom the group consisting of elements belonging to Groups IIIa, IVa, Va,VIa, VIIa, VIII, Ib, IIb and C, in a mixed gas comprising a rare gas andnitrogen; and forming a second barrier layer by sputtering with a targetincluding at least Ge and X in a mixed gas comprising a rare gas andnitrogen; wherein said first barrier layer is formed between saidprotective layer and said recording layer, said protective layercomprises sulfur, said recording layer has a thickness less than orequal to 20 nm and comprises tellurium, said second barrier layer isformed on the recording layer; wherein said first barrier layercomprises at least one selected from the group consisting of GeXN andGeXON as a main component; and wherein a composition ratio of Ge and Xin the target used in forming the first barrier layer is represented byGe_(1-m)X_(m) and a composition ratio of Ge and X in the target used informing the second barrier layer is represented by Ge_(1-n)X_(n), andthe following inequality is satisfied: m<n, where 0<m<1, 0<n<1.